LITERATURE ON THE EYES AND VISION
a. General
Serres, Marcel de. Mémoires sur les yeux composés et les yeux lisses des insectes. Montpellier, 1813.
Müller, Johannes. Zur vergleichenden Physiologie des Gesichtssinnes der Menschen und der Tiere. 8 Taf. Leipzig, 1826.
—— Ueber die Augen des Maikäfers. (Meckel’s Archiv f. Anat. u. Phys., 1829, pp. 177–181; Ann. d. Sc. nat., 1829, sér. 1, xviii, pp. 108–112.)
Dujardin, F. Sur les yeux simples ou stemmates des animaux articulés. (C. R. Acad. Sci., Paris, 1847, xxv, pp. 711–714.)
Gottsche, C. M. Beitrag zur Anatomie und Physiologie des Auges der Krebse und Fliegen. (Müller’s Archiv für Anat. u. Phys., 1852, pp. 483–492. Figs.)
Murray, Andrew. On insect vision and blind insects. (Edinburgh New Phil. Jour., new ser. vi, 1857, pp. 120–138.)
Claparède, Édouard. Zur Morphologie der zusammengesetzten Augen bei den Arthropoden. (Zeitschr. f. wissensch. Zool., 1859, x, pp. 191–214, 3 Taf.)
Dor, H. De la vision chez les Arthropodes. (Archives Sci. Phys, et Nat., 1861, xii, p. 22, 1 Pl.)
Landois, H. Die Raupenaugen (Ocelli compositi mihi). (Zeitschr. f. wissensch. Zool., xvi, 1866, pp. 27–44, 1 Taf.)
—— und W. Thelen. Zur Entwicklungsgeschichte der fasettierten Augen von Tenebrio molitor L. (Zeitschr. f. wissensch. Zool., xvii, 1867, pp. 34–43, 1 Taf.)
Schultze, Max. Untersuchungen über die zusammengesetzten Augen der Krebsen und Insecten. Bonn, 1868.
Schmidt, Oscar. Die Form der Krystallkegel in Arthropodenauge. (Zeitschr. f. wissensch. Zool., xxx, Suppl., 1878, pp. 1–12, 1 Taf.)
Grenacher, H. Untersuchungen ueber das Sehorgan der Arthropoden, insbesondere Spinnen, Insecten und Crustaceen. (Göttingen, 1879, 4º, pp. 1–188, 11 Taf.)
Reichenbach, H. Wie die Insekten sehen. Fig. (Daheim, xvi Jahrg., 1880, pp. 284–286.)
Poletajew, N. Ueber die Ozellen und ihr Sehvermögen bei den Phryganiden. (Horæ Soc. Ent. Ross., 1884, xviii, p. 23, 1 Taf. In Russian.)
Hickson, S. J. The eye and optic tract of insects. (Quart. Journ. Micr. Sc., ser. 2, xxv, 1885, pp. 215–221, 3 Pls.)
Notthaft, Jul. Ueber die Gesichtswahrnehmungen vermittelst des Fazettenauges. (Abhandl. Senckenberg. naturf. Ges., xii., 1880, pp. 35–124, 5 Taf.)
—— Die physiologische Bedeutung des fazettierten Insektenauges. (Kosmos, 1886, xviii, pp. 442–450, Fig.)
Mark, E. L. Simple eyes in arthropods. (Bull. Mus. Comp. Zool., 1887, xiii, pp. 49–105, 5 Pls.)
Girschner, E. Einiges über die Färbung der Dipterenaugen. (Berlin. Ent. Zeitschr., 1888, xxxi, pp. 155–162, 1 Taf.)
Graber, V. Das unicorneale Tracheatenauge. (Archiv f. Mikroskop. Anat., xvii, 1879, pp. 58–93, 3 Taf.; Nachtrag, p. 94.)
—— Fundamentalversuche über die Helligkeits- und Farbenempfindlichkeit augenloser und geblendeter Tiere. (Sitzgs.-Ber. Akad. Wissensch., Wien, 1883, lxxxvii, pp. 201–236.)
Dahl, Fr. Die Insekten können Formen unterscheiden. (Zool. Anz., xii, 1889, pp. 243–247.)
Ciaccio, G. V. Figure dichiarative della minuta fabbrica degli occhi de’ Ditteri. Bologna, 1884, 12 Taf., 30 pp.
—— Della minuta fabbrica degli occhi de’ Ditteri. (Mem. Accad. Bologna, 1886, ser. 4, vi, pp. 605–660.)
—— Sur la forme et la structure des facettes de la cornée et sur les milieux refringents des yeux composés des Muscidés. (Journ. Micr., Paris, 1889, xiii Année, pp. 80–84.)
Carrière, J. On the eyes of some invertebrata. (Quart. Journ. Micr. Sc. 1884, ser. 2, xxiv, pp. 673–681, 1 Pl.)
—— Ueber die Arbeiten von Viallanes, Ciaccio und Hickson. (Biolog. Centralblatt, v, 1885, pp. 589–597.)
—— Die Sehorgane der Tiere vergleichend anatomisch dargestellt. München u. Leipzig, 1885, 205 pp., 147 Figs., 1 Taf.
—— Kurze Mitteilungen aus fortgesetzten Untersuchungen über die Sehorgane. (Zool. Anz., ix Jarhg., 1886, pp. 141–147, 479–481, 496–500.)
Forel, A. Les fourmis de la Suisse. (Neue Denkschriften der schweiz. naturforsch. Gesellsch. xxvi. 1874, pp. 480, 2 Pls.) Separate. pp. iv u. 457. Genève.
—— Beitrag zur Kenntnis der Sinnesempfindungen der Insekten. (Mitteil. d. Münchener Ent. Vereins, ii Jahrg., 1878, pp. 1–21.)
—— Sensations des insectes. (Recueil Zool. Suisse, iv, 1886 et 1887.)
Plateau, F. L’instinct chez les insectes mis en défaut par les fleurs artificielles? (Assoc. française avancement des sciences. Congrès de Clermont. Ferrand, 1876.)
Plateau, F. Recherches expérimentales sur la vision chez les insectes. Les insectes distinguent-ils la forme des objets? (Bull. Acad. Belg. 3 Sér. x, 1885, pp. 231–250.)
—— Recherches expérimentales sur la vision chez les insectes.
1. Part, a. Résumé des travaux effectués jusqu’en 1887 sur la structure et le fonctionnement des yeux simples. b. Vision chez les Myriapodes. (Ibid. Sér. 3, xiv, 1887, pp. 407–448, 1 Pl.)
3. Part, a. Vision chez les chenilles, b. Rôle des ocelles frontaux chez les insectes parfaits. (Ibid. Sér. 3, xv, 1888, pp. 28–91.)
4. Part. Vision à l’aide des yeux composés. a. Résumé anatomo-physiologique. b. Expériences comparatives sur les insectes et sur les vertébrés. (Mém. cour. et autres Mém. Acad. Belg. 1888, xliii, pp. 1–91, 2 Pls.)
5. Part, a. Perception des mouvements chez les insectes. b. Addition aux recherches sur le vol des insectes avenglés. c. Résumé général. (Bull. Acad. Belg. 1888, sér. 3, xvi, pp. 395–457, 1 Pl.)
—— Recherches expérimentales sur la vision chez les Arthropodes, 2 Pls. (Mém. couronn. et autres Mém. publ. p. l’Acad. Roy. d. Sciences, etc., de Belgique, xliii, Bruxelles, 1889.)
Watase, S. On the morphology of the compound eyes in the Arthropoda. (Studies from biol. laborat. Johns-Hopkins Univ., 1890, pp. 287–334, 4 Pls.)
Stefanowska, M. La disposition histologique du pigment dans les yeux des Arthropodes. (Recueil Zool. Suisse, 1890, pp. 151–200, 2 Pls.)
Pankrath, O. Das Auge der Raupen und Phryganiden larven. (Zeitschr. f. wissensch. Zool., 1890, xlix, pp. 690–708, 2 Taf.)
Lowne, B. Th. On the modifications of the simple and compound eyes of insects. (Philos. Trans. Roy. Soc., London, clxix, 1878, pp. 577–602, 3 Pls.)
—— On the structure and functions of the eyes of Arthropoda. (Proc. Roy. Soc., London, 1883, xxxv, pp. 140–145.)
—— On the compound vision and the morphology of the eye in insects. (Trans. Linn. Soc., London, 1884, ii, pp. 389–420, 4 Pls.)
—— On the structure of the retina of the blow-fly (Calliphora erythrocephala). (Jour. Linn. Soc., London, 1890, xx, pp. 406–417, 1 Pl.)
Patten, W. Eyes of molluscs and arthropods. (Journal of Morphol., Boston, 1887, i, pp. 67–92, 1 Pl.; Mitteil. Zool. Stat. Neapel, vi, 1886, pp. 542–756, 5 Taf.)
—— Studies on the eyes of arthropods.—1. Development of the eyes of Vespa, with observations on the ocelli of some insects. (Ibid., pp. 193–226, 1 Pl.)—2. Eyes of Acilius. (Ibid., 1888, ii., pp. 190–97, 7 Pls.)
—— On the eyes of molluscs and arthropods. (Zool. Anzeiger, 1887, x Jahrg., pp. 256–261.)
—— Is the ommatidium a hair-bearing sense-bud? (Anatom. Anzeiger, 1890, v, pp. 353–359, 4 Figs.)
Exner, S. Ueber das Sehen von Bewegungen und die Theorie des zusammengesetzten Auges. (Sitzgsber. d. math. naturwiss. Cl. kais. Akad. d. Wissens. Wien, lxxii Jahrg., 1875, 3 Abt. Physiologie, pp. 156–190, 1 Taf.)
—— Die Frage von der Funktionsweise der Fazettenauges. (Biolog. Centralblatt, i, 1881, pp. 272–281.)
—— Das Netzhautbild des Insektenauges. (Sitzgsber. kais. Akad. d. Wissensch. Wien, 1889, xcviii, 3 Abt., pp. 13–65, 2 Taf. u. 7 Figs.)
—— Durch Licht bedingte Verschiebungen des Pigmentes im Insektenauge und deren physiologische Bedeutung. (Ibid., pp. 143–151, 1 Taf.)
Exner, S. Die Physiologie der fazettierten Augen von Krebsen und Insekten, 7 Taf., 1, Lichtdruck u. 23 Holzschn. pp. 206. Wien, F. Deuticke, 1891.
Lubbock, John. On the senses, instincts, and intelligence of animals, with special reference to insects. London, 1888, pp. 292.
Mallock, A. Insect sight and the defining power of composite eyes. (Proc. Roy. Soc., London, 1894, lv, pp. 85–90, 3 Figs.)
b. The color-sense
Nussli, J. Ueber den Farbensinn der Bienen. (Schweiz. Bienenzeitung, N. F., ii Jahrg., 1879, pp. 238–240.)
Kramer. Der Farbensinn der Bienen. (Ibid., iii Jahrg., 1880, pp. 179–198.)
Gross, Wilhelm. Ueber den Farbensinn der Tiere, insbesondere der Insekten. (Isis v. Russ., v Jahrg., 1880, pp. 292–294, 300–302, 308–309.)
Lubbock, John. Ants, bees, and wasps. London, 1882, pp. 448. Also On the senses, etc., of animals, 1889.
Graber, Vitus. Grundlinien zur Erforschung des Helligkeits und Farbensinnes der Tiere. Prag u. Leipzig, 1884, pp. 322. (See also p. 262.)
Forel, Auguste. Les Fourmis perçoisent-elles l’ultra-violet avec leurs yeux ou avec leur peau? (Arch. Sci. Phys. Nat. Genève, 1886, 3 sér., xvi, pp. 346–350.)
Also the works of Darwin, Wallace, F. Müller, Grant Allen’s The Color Sense (1879), Beddard’s Animal Coloration, etc.
b. The organs of smell
The seat of the organs of smell is mainly in the antennæ, and they may be regarded as the principal olfactory organs. For our present knowledge of the anatomy and physiology of the olfactory organs of insects we are mainly indebted to the recent investigations of Hauser and of Kraepelin. The following historical and critical remarks are translated from Kraepelin’s able treatise:
Historical sketch of our knowledge of the organs of smell.—In the first half of the last century began the inquiries as to the seat of the sense of smell in the arthropods. Thus Réaumur, in his Mémoires (i, p. 283; ii, 224), expressed the view that in the antennæ was situated a special organ which might be an organ of smell.
Lesser, Roesel, Lyonet, Bonnet, and others expressed the same opinion. Before this Sulzer suggested that an “unknown sense” might exist in the antennæ; others regarded the stigmata as organs of smell, as these were considered the natural passages for the olfactory currents. Duméril, in two special treatises as well as in his Considérations générales, sought to prove the theory as to the seat of the organs of smell in the stigmata.
Against both of these leading views as to the seat of the sense of smell were expressed, in the last century, different opinions. Thus Comparetti thought that the sense of smell might be localized in very different points of the head, in the antennal club of lamellicorns, in the sucking-tube of Lepidoptera, in special frontal holes of flies and Orthoptera, etc., while Bonsdorf considered the palpi as organs of smell.
Thus four different views, confused, were held at the opening of this century; the Hamburg zoölogist, M. C. S. Lehrman, in three different treatises, brought together all the hitherto known observations and arguments, treated them critically, and completed them by his own extended studies. Lehrman adopted the opinions of Reimarus, Baster, Duméril, and Schelver, that the stigmata presented the most convenient place for the site of the organs of smell. Cuvier followed throughout the lead of Lehrman, but Latreille returned to the view of the perception of smell by the antennæ, while Treviranus considered the mouth of arthropods as the probable site of the sense of smell, an opinion which, before his time, Huber, in his experiments on bees, had thought to be correct. Marcel de Serres (1811) returned again to the palpi, and asserted—at least in the Orthoptera—their functions to be olfactory, while Blainville, ten years later, again expressed anew the old opinion that the antennæ, or at least their terminations, were organs of smell. Up to that date there was an uncertainty as to the seat of the organs both of smell and hearing. Fabricius, indeed, had already, in 1783, thought he had found an organ of hearing at the base of the outer antenna. In 1826 J. Müller mentioned an already well-known organ in the abdomen of crickets as an organ of hearing. Müller, however, was doubtful, from the fact that the nerve passing to this organ arose, not from the brain, but from the third thoracic ganglion; but, notwithstanding, he remarks: “Perhaps we have not found the organ of hearing in insects because we sought for it in the head.” This discovery was afterwards considerably broadened and extended by Siebold’s work, for the views of these naturalists on the seat of both organs had a definite influence, especially in Germany. For awhile, indeed, Müller’s hypothesis stood in complete contradiction, so that during the following decennial was presented anew the picture of opposing observations and opinions as to the nature of the organs of smell. While Robineau-Desvoidy, at the end of the twentieth year, and also later, in different writings, strove energetically for the olfactory nature of the antennæ, Straus-Dürckheim held fast to the view that the tracheæ possessed the function under discussion. At the same period Kirby and Spence, in their valuable Introduction to Entomology, maintained that “two white cushions on the under side of the upper lip” in the mouth of biting insects formed a nose or “rhinarium” peculiar to insects. This opinion was afterwards adopted by Lacordaire (Introduction à Entomologie), and also by Oken in his Lehrbuch der Naturphilosophie, while Burmeister, rejecting all the views previously held, believed that insects might perhaps smell “with the inner upper surface of the skin.” Müller’s locust’s ear he regarded as a vocal organ.
Besides these occasional expressions of opinion, the French literature of the thirtieth and fortieth years of this century recorded a long series of special works, with weighty experimental and physiological contents, on this subject. Thus Lefebre, in 1838, described the experiments which he made on bees, and which seemed to assign the seat of the sense of smell to the antennæ. Dugès reported similar researches on the Scolopendræ, and Pierret thought that the great development of the antennæ in the male Bombycidæ might be similarly interpreted. Driesch sought to give currency to the views of Bonsdorf, Lamarck, and Marcel de Serres, that the sense of smell was localized in the palpi, though Duponchel went back to the old assertion of æroscepsis of Lehrman, i.e. of the air-test through the antennæ, and Goureau again referred the seat of the sense of smell to the mouth. In England, Newport at this period put forth a work in which he considered the antennæ as organs of touch and hearing, and the palpi as organs of smell—a view which, as regards the antennæ, was opposed by Newman.
Thus the contention as to the use of the antennæ and the seat of the organs of smell and hearing fluctuated from one side to the other, and when in 1844 Küster, by reason of his experiments on numerous insects, again claimed that “the antennæ are the smelling organs of insects,” he argued on a scientific basis; yet v. Siebold and Stannius (1848), in their valuable Lehrbuch der vergleichenden Anatomie (p. 581), remarked that “organs of smell have not yet with certainty been discovered in these animals.”
The following decennial was of marked importance in the judgment of many disputed questions. Almost contemporaneously with Siebold and Stannius’ Lehrbuch appeared an opportune treatise by Erichson, in which this naturalist first brought forward certain anatomical data as to the structure of the antennæ of insects. In a great number of insects Erichson described on the upper surface of the antennæ peculiar minute pits, “pori,” which, according to him, were covered by a thin membrane, and to which he ascribed the perception of smell. A still more thorough work on this subject was published in the following year by Burmeister, who recognized in the pits of lamellicorns many small tubercles and hairs; and about the same time Slater, as also Pierret and Erichson before him had done, out of the differences of the antennal development in the males and females in flesh and plant-eating insects, brought together the proof of the olfactory function of the antennæ. But the most valuable work of this period is that of Perris, who, after a review of previous opinions, by exact observations and experiments, a model of their kind, sought to discover the seat of the sense of smell. He comes to the conclusion that the antennæ, and perhaps also the palpi, may claim this sense, and finds full confirmation of Dufour’s views, and adopts as new the physiological possibility expressed by Hill and Bonnet, that the antennæ might be the seat of both senses—those of smell and hearing.
The beautiful works of Erichson, Burmeister, and Perris could not remain long unnoticed. In 1857 Hicks published complete researches on the peculiar nerve-endings which he had found in the antennæ, also in the halteres of flies and the wings of all the other groups of insects, and which he judged to be for the perception of smell. But Erichson’s and Burmeister’s “pori” were by Lespès, in 1858, explained to be so many auditory vesicles with otoliths. This view was refuted by Claparède and Claus without their deciding on any definite sense. Leydig first made a decided step in advance. In different writings this naturalist had busied himself with the integumental structures of arthropods, and declared Erichson’s view as to the olfactory nature of the antennal pits as the truest, before he, in his careful work on the olfactory and auditory organs of crabs and insects, had given excellent representations of the numerous anatomical details which he had selected from his extensive researches in all groups of arthropods. Besides the pits which were found to exist in Crustacea, Scolopendræ, beetles, Hymenoptera, Diptera, Orthoptera, Neuroptera, and Hemiptera, and which had only thus far been regarded as sense-organs, Leydig first calls attention to the widely distributed pegs and teeth, also considering them as sense-organs. “Olfactory teeth,” occurring as pale rods, perforated at the end, on the surface of the antennæ of Crustacea, Myriopoda, Hymenoptera, Lepidoptera, Coleoptera, are easily distinguished, and besides the “olfactory pegs” of the palpi, may be claimed as organs of smell. The nerve-end apparatus first discovered by Hicks in the halteres and wings, Leydig thinks should be ranked as organs of hearing.
There was still some opposition to Leydig’s opinion that in the insects the sense of smell is localized in the antennæ (teeth and pits), and here the work of Hensen might be mentioned, which in 1860 had a decided influence upon the conclusion of some inquiries.
Thus Landois denied that the antennæ had the sense of smell, and declared that the pits in the antennæ of the stag beetle were auditory organs. So, also, Paasch rejected Leydig’s conclusion, while he sought to again reinstate the old opinion of Rosenthal as to the olfactory nature of the frontal cavity of the Diptera. In spite of the exact observations and interesting anatomical discoveries of Forel in ants, made in 1874, there appeared the great work of Wolff on the olfactory organs of bees, in which this observer, with much skill and acuteness, sought to give a basis for the hypothesis of Kirby and Spence that the seat of the sense of smell lay in the soft palatine skin of the labrum within the mouth (i.e. the epipharynx). Joseph, two years later, drew attention to the stigmata as olfactory organs, referring to the olfactory girdle, and Forel sought by an occasional criticism of Wolff’s conclusions to prove experimentally the olfactory function of the antenna; but Graber, in his widely read book on insects, defended the Wolffian “nose” in the most determined way, and denied to the antennæ their so often indicated faculty of smell. In 1879 Berté thought he had observed in the antenna of the flea a distinct auditory organ, and Lubbock considered the organs of Forel in the antennæ of ants as a “microscopic stethoscope.” In 1879 Graber described a new otocyst-like sense-organ in the antennæ of flies, which was accompanied by a complete list of all the conceivable forms of auditory organs in arthropods. In this work Graber described in Musca and other Diptera closed otocysts with otoliths and auditory hairs, as Lespès had previously done. But Paul Mayer, in two essays, refuted this view in a criticism of the opinion of Berté, referring the “otocysts with otoliths” to the well-known antennal pits into which tracheæ might pass. Mayer did not decide on the function of the hairs which extend to the bottom of the pits; while in the most recent research, that of Hauser, the author again energetically contended for the olfactory function of the antennæ. Both through physiological experiments and detailed anatomical investigations Hauser sought to prove his hypothesis, as Pierrot, Erichson, Slater, and others had done before him, besides working from an evolutional point of view. In a purely anatomical aspect, especially prominent are his discovery of the singularly formed nerve-rods in the pits and peg-like teeth of the Hymenoptera and their development, as well as the assertion that numerous hairs in the pits described by Leydig, Meyer, etc., should be considered as direct terminations of nervous fibres passing into the pits. In the pits he farther, with Erichson, notices a serous fluid, which may serve as a medium for the perception of smells. Among the latest articles on this subject are those of Künckel and Gazagnaire, which are entirely anatomical, while the latest treatise of Graber on the organs of hearing in insects opposes Hicks’s theory of the olfactory function of the nerve-end apparatus in the halteres, wings, etc., and argues for the auditory nature of these structures. Finally, according to Voges, the sense of smell is not localized, but spread over the whole body.
My own observations on different groups of insects agree, in general, with those of Perris, Forel, and Hauser, without being in a position to confirm or deny the varying relations of the Hemiptera. That irritating odorous substances (chloroform, acetic acid) cause the limbs to move in sympathy with the stimulus, I have seen several times in Acanthosoma; still it may be a gustatory rather than olfactory stimulus.
Turning now from speculation and simple observation to exact anatomical and histological data, the nerve-end apparatus seems to have a distinct reference to the perception of odors. It comprises a structure composed of nervous substances which are enclosed in a chitinous tube, and either only stand in relation to the surrounding bodies by the perforated point, or pass to the surface as free nerve-fibrillæ.
In insects there is a remarkable and fundamental difference in the structures of the parts supposed to be the organs of smell. Erichson was acquainted only with the “pori” covered by a thin membrane; but Burmeister, in his careful work on the antennæ of the lamellicorns, distinguished pits at the bottom of which hairs rise from a cup-like tubercle, from those which were free from hairs. Leydig afterwards was the first to regard as olfactory organs the so-called pegs (kegel), a short, thick, hair-like structure distinctly perforated at the tip, which had already, by Lespès in Cercopis, etc., been described as a kind of tactile papilla. Other very peculiar olfactory organs of different form, Forel (Fourmis de la Suisse) discovered in the antennæ of ants, which Lubbock incorrectly associated with the nerve-end apparatus found by Hicks in other insects.
As the final result of his researches Kraepelin states that the great variety of antennal structures previously described may be referred to a single common fundamental type of a more or less developed free or sunken hair-like body which stands in connection by means of a wide pore-canal with a many-nucleated ganglion-cell. The latter sends only a relatively slender nerve-fibre (axial cord) through the pore-canal into the hair; but the same is enclosed by epithelial cells which surround the pore-canal.
Hauser’s researches on the organs of smell in insects were so carefully made and conclusive that our readers will, we feel sure, be glad to have laid before them in detail the facts which prove so satisfactorily that the antennæ of most insects are olfactory rather than auditory in their functions.
Physiological experiments.—First of all one should observe as exactly as possible the normal animal in its relation to certain odorous substances, whose fumes possess no corrosive power or peculiarities interfering with respiration; then remove the antennæ and try after several days to ascertain what changes have taken place in the relation of the animal to the substance. In order to come to no false results it is often necessary to let the insects operated upon rest one or two days, for immediately after the operation they are generally so restless that a careful experiment is impossible.
The extirpation of the antennæ is borne by different insects in different ways; many bear it very easily, and can live for months after the operation, while others die in the course of a few days after the loss of these appendages. The animals seem to be least injured if the operation is performed at a time when they are hibernating. Pyrrhocoris apterus, and many other insects, afforded a very striking proof of this relation.
Experiments made by placing the antennæ in liquid paraffine so as to cover them with a layer of paraffine, thus excluding the air, gave the same result as if the antennæ had been removed.
The experiments may be divided, according to their object, into three groups. Experiments of the first kind were made on insects in their relation to strong-smelling substances, as turpentine, carbolic acid, etc., before and after extirpation of the antennæ. The second group embraces experiments on the relation of animals as regards their search for food; and finally the third group embraces experiments on the relation of the sexes relative to reproduction before and after the extirpation of the antennæ.
Relation of insects to smelling substances before and after the loss of their antennæ.—Taking a glass rod dipped in carbolic acid and holding it within 10 cm. of Philonthus œneus, found under stones at the end of February, it was seen to raise its head, turn it in different directions, and to make lively movements with its antennæ. But scarcely had Hauser placed the rod close to it when it started back as if frightened, made a sudden turn, and rushed, extremely disturbed, in the opposite direction. When he removed the glass rod, the creature busied itself for some time with its antennæ, while it drew them, with the aid of its fore limbs, through its mouth, although they had not come into direct contact with the carbolic acid. There was the same reaction against oil of turpentine, and it was still more violent against acetic acid.
After having many times carefully tested the relations of the normal animal to the substances mentioned, the antennæ were removed from the socket-cavity.
On the second day after Hauser experimented with the insects, they exhibited no reaction either against the carbolic acid, the oil of turpentine, or even against the acetic acid, although he held the glass rod which had been dipped into it for one or two minutes before and over the head. The creatures remained completely quiet and immovable, at the most slightly moving the palpi. They showed otherwise no change in their mode of life and their demeanor; they ate with great eagerness flesh which had been placed before them, or dead insects, and some were as active as usual as late as May. These beetles had, as proved by the experiments, lost the sense of smell alone; how far the sense of touch was lost Hauser could not experimentally decide.
The same results followed experiments with species of the genus Ptinus, Tenebrio, Ichneumon, Formica, Vespa, Tenthredo, Saturnia, Vanessa, and Smerinthus; also many species of Diptera and Orthoptera, besides Julus and Lithobius, while many larvæ reacted in the same manner.
Less satisfactory were the experiments with Carabus, Melolontha, and Silpha; there is no doubt that the species of these genera, through the extirpation of their antennæ, become more or less injured as to the acuteness of their powers of smelling; but they never show themselves wholly unable to perceive strong-smelling substances.
The allurement of the substance acts for a longer time on those deprived of their antennæ, then they become restless, then they wander away from the glass tube held before them; still all their movements are but slightly energetic, and the entire reaction is indeterminate and enfeebled.
Experiments with the Hemiptera gave still more unfavorable results; after the loss of their antennæ they reacted to smells as eagerly as those did which were uninjured.
Experiments on the use of the antennæ in seeking for food.—Under this head experiments were made with Silpha, Sarcophaga, Calliphora, and Cynomyia.
Silpha and its larva were treated in the following manner: they were placed in large boxes whose bottoms were covered with moss, etc.; in a corner of the box was placed a bottle with a small opening, in which was placed strong-smelling meat. So long as the beetles were in possession of their antennæ they invariably after a while discovered the meat exposed in the bottle, while after the loss of their antennæ they did not come in contact with it.
In a similar way acted the species of Sarcophaga, Calliphora, and Cynomyia. Hauser, in experimenting with these, placed a dish with a large piece of decayed flesh on his writing-table. In a short time specimens of the flies referred to entered through the open window of the room. The oftener he drove them away from the meat would they swarm thickly upon it. Then closing the window and catching all the flies, he deprived them of their antennæ and again set them free. They flew about the room, but none settled upon the flesh nor tried to approach it. Where a fly had alighted on a curtain or other object, the decayed flesh was placed under it so that the full force of the effluvium should pass over it, but even then no fly would settle upon it.
Experiments testing the influence of the antennæ of the males in seeking the females.—For this purpose Hauser chose those kinds in which the male antennæ differ in secondary sexual characters from those of the female, and in which it is known that they readily couple in confinement, as Saturnia pavonia, Ocneria dispar, and Melolontha vulgaris. The two first-named insects did not couple after the extirpation of their antennæ. Of Melolontha vulgaris twenty pairs were placed in a moderately sized box. On the next morning twelve pairs of them were found coupling. Hauser then, after removing the first lot, placed a new set of thirty pairs in the same box, cut off all the antennæ of the males and those of a number of females. On the following morning only four pairs were found coupling, and at the end of three days five others were observed sexually united.
From these experiments Hauser inferred that those insects deprived of their antennæ were placed in the most favorable situation, such as they would not find in freedom; for the space in which the insects moved about was so limited that the males and females must of necessity meet. But at the same time the results of the experiments cannot absolutely be regarded as proving that the males, after the loss of their antennæ, were then not in condition to find the females, because in the case of the above-mentioned moths, under similar conditions, after the extirpation of the antennæ no sexual union took place. If, however, the experiments made do not all lead to the results desired, Hauser thinks that the results agree with those of his histological researches, that in the greater number of insects the sense of smell has its seat in the antennæ. His results also agree with those of Perris.
Structure of the organs of smell in insects.—The olfactory organs consist, in insects,—i.e., all Orthoptera, Termitidæ, Psocidæ, Diptera, and Hymenoptera, also in most Lepidoptera, Neuroptera, and Coleoptera,—
1. Of a thick nerve arising from the brain, which passes into the antennæ.
2. Of a sensitive apparatus at the end, which consists of staff-like cells, which are modified hypodermis cells, with which the fibres of the nerves connect.
3. Of a supporting and accessory apparatus, consisting of pits, or peg- or tooth-like projections filled with a serous fluid, and which may be regarded as invaginations and outgrowths of the epidermis.
Hauser adds a remark on the distribution of the pits and teeth in the larvæ of insects, saying that his observations are incomplete, but that it appears that in the larvæ the teeth are most generally distributed, and that they occur not on the antennæ alone, but on the palpi; but in very many larvæ neither pits nor teeth[[47]] occurred. In the Myriopoda teeth-like projections occur on the ends of the antennæ. In Lithobius they form very small, almost cylindrical, pale organs.
Fig. 268.—Olfactory organ of Caloptenus.
Fig. 269.—Olfactory pits of the antenna of Stenobothrus. This and Fig. 268 after Hauser.
Lettering for Figs. 268, 269, 273, 275, 276, 278–281.—a, a, circular thickening of the skin surrounding the opening of the olfactory pit; ax, thread-like continuation of the nerve-cell; b, vesicle-like bottom of the olfactory pit, through which the olfactory style passes; br bristle in Fig. 283, stout, and protecting the olfactory pit; bs, bent bristle or seta; ch, chitinous integument of the antennæ; d, seen in section; f, invaginated pit; Fv, Forel’s flask-shaped organ; Fvo, its opening seen from the surface; gl, gland-like mass of cells; hyc, hypodermic cells; i, entrance into the canal belonging to the pit; m, olfactory membrane; m′, m″, mc, membrane-forming cell; n, nerve of special sense; nc, nucleus of the sense- or ganglion-cell; o, opening into the olfactory pit; p, olfactory pit; cp, compound pits; pw, wall of the pit; s, a large seta; sc, sense- or ganglion-cell; st, olfactory or sense-style, sometimes peg-shaped; tb, tactile bristle.
Fig. 270.—A, b, sense-organ on the abdominal appendages of a fly (Chrysopila); c, sense-organ on the terminal joint of palpus of Perla.
Fig. 271.—Longitudinal section of part of cercus of Acheta domestica: ch, cuticula; hyp, hypodermis; n. nerve; h′1, integumental hairs, not sensory; h2, ordinary hair; h3, sensory hair; h4, bladder-like hair; sz, sense-cell.—After Vom Rath, from Sharp.
In the course of a special description of these sense-organs in the Orthoptera, Hauser describes at length those of Œdipoda cœrulescens and Caloptenus italicus. On one antennal joint of Caloptenus (Fig. 268) was often counted 50 pits; on the anterior joints the number diminishes to about 30. Hauser thinks that in all Orthoptera whose antennæ are like those of Caloptenus occur similar pits, as he found them in Stenobothrus (Fig. 269) as well as in Œdipoda. Gryllotalpa possesses similar pits,—four to six on each antennal joint, making between 300 and 400 pits on each antenna.[[48]] In Mantis religiosa the pits were not detected, but on each joint, except the eighth basal, there are about 200 small, hollow, curved teeth with a fine opening in front.
In the Neuroptera (Chrysopa) there occur on the antennæ, besides numerous very long tactile bristles, small pale, transparent teeth. No pits could be detected.
In the Hemiptera (two species of Pyrrhocoris only were examined) only two kinds of tactile bristles occurred, but Hauser detected no pits, though Lespès states that they are present.
Fig. 272.—Longitudinal section of apex of palpus of Pieris brassicæ: sch, scales; ch, cuticula; hyp, hypodermis; n, nerve; sz, sense-cells; sh, sense-hairs.—After Vom Rath, from Sharp.
Of the Diptera, Hauser examined more than 60 species. The pits in the Diptera brachycera (Muscidæ, etc.) are unexceptionally confined to the third antennal joint. Their number varies extraordinarily in the different species. Helophilus florens has on each antennal disk only a single pit, while Echinomyia grossa possesses 200 of them. In flies of certain families the pits are compound, and contain 10, 20, and often 100 olfactory hairs, partly arising from the coalescence of several pits. Such pits are usually divided by lateral walls into several chambers, whose connection is only indicated by their common outlet. Simple olfactory pits with a single olfactory style were observed only in the Tabanidæ, Asilidæ, Bombylidæ, Leptidæ, Dolichopidæ, Stratiomyidæ, and Tipulidæ. In the last the compound forms do not occur at all, but in the other families mentioned also occur compound pits, receiving from two to ten nerve-terminations.
The antennal pits of flies are always sac-like invaginations of the external chitinous integument, of manifold shapes, opening externally and never closed by a membrane. The pits differ but slightly in the different species, and that of Cyrtoneura stabulans (Fig. 273) is described at length as typical of those of brachycerous flies in general.
The olfactory pits of the Tipulidæ seem to have a somewhat different structure, since the external passage is closed. It is circular, surrounded with a slight chitinous wall, and not covered with bristles. Such pits in their external appearance are like those of the locust (Caloptenus) and many Hymenoptera. They are situated usually on the third antennal joint. Pachyrhina pratensis L. has about 60 of them, as have Tipula oleracea L. and Ctenophora.
In the Lepidoptera, olfactory pits are much like those of flies. Hauser describes in detail those of Vanessa io. Those of the moths were not examined, but they can be readily and satisfactorily proved to be the site of the olfactory sense.
Fig. 273.—Longitudinal section through the third antennal joint of a fly (Cyrtoneura stabulans), showing the compound pits from above and in section.—After Hauser.
Fig. 274.—Antenna of Adelops, showing the olfactory organs (p) in the five last joints.
Historical researches in respect to the Coleoptera generally gave a very unfavorable result, contrary to Lespès’s views. That author states that in the Carabidæ the pits are found on the four first joints, but Hauser could discover them in none which he examined. Usually only tactile bristles occur, so also in the Cerambycidæ, Curculionidæ, Chrysomelidæ, and Cantharidæ. In a blind silphid beetle (Adelops hirtus) of Mammoth Cave we have found well-marked olfactory organs (Fig. 274). Similar organs occur in the antennæ of the Panorpidæ.
Olfactory pits, however, without doubt occur in Silpha, Necrophorus, Staphylinus, Philonthus, and Tenebrio. The openings of the pits are small and surrounded with a small chitinous ring; in Silpha, Necrophorus, and Tenebrio they cannot easily be distinguished from the insertion-cavities of the bristles, but in Philonthus and Staphylinus they are less like them, being distinguished by their somewhat larger size and their often more oval form. In Philonthus æneus about 100 such small pits occur irregularly on the terminal joints; besides, in this species on each side of the terminal joint is an apparatus which is like the compound pit generally occurring in the Diptera.
Fig. 275.—Olfactory pits of the antenna of Melolontha vulgaris.—After Kraepelin.
Fig. 276.—Antennal pit of Melolontha vulgaris, seen in vertical section.—After Hauser.
Very remarkable pits occur in the antennal lamellæ of Melolontha vulgaris (Fig. 275) and other lamellicorns. On the outer surface of the first and seventh (in the female the sixth) antennal leaf, as also on the edges of the other leaves, only arise scattered bristles; on the inner surface of the first and seventh leaves, as also on both surfaces of the second to sixth leaves, are close rows of rather shallow depressions of irregular form, some circular, others regularly hexagonal. Their number is enormous: in the males 39,000, in the females about 35,000, occur on each antenna.
Fig. 277.—Organ of smell of Anophthalmus.—After Hauser. A, a, b, the same in A. tenuis, B in A. tellkampfii.
Fig. 278.—Section through antennal joint of Vespa crabro, showing the great number of olfactory pits, olfactory and tactile bristles. A, section through an olfactory pit of Vespa crabro.—After Hauser.
The antennal pits and teeth of Dyticus marginalis are morphologically and physiologically identical with those of bees and wasps. In Anophthalmus bilimekii, Hauser found on the last antennal joints about 60 teeth, which essentially differ in form from those previously described; they are very pale, transparent, cylindrical, elongated, and bent elbow-shaped on the first third, so that the last two-thirds run parallel with the antenna. The length of these remarkable teeth is 0.035 mm., their breadth 0.005 mm. He only found them in Anophthalmus, and in no other species of Carabidæ; they must resemble the teeth described in Chrysopa. Our species possesses similar processes (Fig. 277). Similar teeth occur on the maxillary and labial palpi of beetles. Dyticus marginalis possesses at the end of each terminal palpal joint a group of very small teeth, which were also detected in Anophthalmus bilimekii, Melolontha vulgaris, etc. In Carabus violascens were detected on the maxillary palpi large, plainly microscopical, white disks, which are surrounded with a great number of extremely small teeth.
Whether the above-described organs on the palpi of beetles should be considered as olfactory or gustatory in their nature can only be determined by means of physiological experiments; they probably receive taste-nerve terminations.
Fig. 279.—Olfactory pits of the antenna of Vespa vulgaris.—After Kraepelin.
The Hymenoptera furnished very good material for histological purposes, so that Hauser could not only study the terminal apparatus of the olfactory nerves in the perfect insect, but also in three different stages of the pupa. These are described at length, as regards the distribution of the pits and teeth, in Vespa crabro; each joint of the antenna (flagellum) possesses between 1300 and 1400 pits, nearly 60 teeth, and about 70 tactile hairs; on the terminal joint there are more than 200 teeth, so that each antenna has between 13,000 and 14,000 olfactory pits and about 700 teeth (Kegeln). Fig. 278 represents a cross-section through the penultimate antennal joint of Vespa crabro; we can see how thick are the series of openings on the surface of the antennæ, and how regular is the distribution of the teeth.
The distribution of the olfactory pits and olfactory teeth is thus seen to be very general; the deviations are so insignificant that there is no reason for the establishment of more than one type.
Antennal pits with a small crevice-like opening occur in genera nearly allied to Vespa and also in most Ichneumonidæ, Braconidæ, and Cynipidæ. But the crevice-like openings in these families are considerably longer and often are of a somewhat twisted shape. In all the species with translucent antennæ we can recognize the inner mouth of the pit as a round or nearly round disk situated usually under the middle of the opening. The antennal pits of Apis mellifica, as well as those of Bombus (Fig. 280) and allied genera, differ from those of the Ichneumonidæ in being not like crevices, but circular openings.
Fig. 280.—Olfactory pits of the antenna of Bombus.—After Kraepelin.
Fig. 281.—Olfactory pits of the antenna of Formica: Fv, Hicks’ “bottle,” Forel’s flask-shaped organ, Fvo, its opening.—After Kraepelin.
Fig. 282.—Supposed olfactory organs at end of antenna of Campodea: A, C. staphylinus. B, C. cookei, from Mammoth Cave.
Fig. 283.—Vertical section through a single olfactory pit in the antenna of the horse-fly (Tabanus bovinus). For lettering see p. 272.—After Hauser.
The distribution of the olfactory peg or tooth-like projections seems to be much more limited than that of the pits in the Ichneumonidæ. Hauser could not find any. Apis mellifica possesses on each antennal joint only about twenty slender pale teeth, scarcely a third as many as in Vespa crabro; on the other hand, Formica, of which genus several species were examined, seems to have far more teeth than pits; they are relatively long, pale, transparent, and somewhat clavate; they are not unlike those of Chrysopa; on the terminal joint only occur the round openings (Fvo), which lead into a bottle-shaped invagination of the integument (Fv) and contain an olfactory style (Fig. 281). In the Tenthredinidæ only teeth and no pits were to be detected. Sirex has on the under side of the nine last joints of each antenna a group of from 200 to 300 small teeth, which resemble those of Vespa crabro; Lyda has on the terminal joints about 100 teeth. We may add that supposed organs of smell occur on the antennæ of Campodea (Fig. 282).
Kraepelin also thus briefly summarizes Hauser’s statements as to the forms of the different organs of smell.
The manifold nature of the antennal organs has, by Hauser, from thorough studies of the nerve-elements belonging to them, been not simplified but rendered more complicated. According to this naturalist we may distinguish the following forms which the olfactory organs may assume: 1. “Pale, tooth-like chitinous hairs on the outer surface of the antennæ, which are perforated at the end; nothing is known as to the relation of the nerve passing into it (Chrysopa, Anophthalmus). 2. In pit-like depressions of the antennæ arise nerve-rods (without a chitinous case) which stand in direct relation with a ganglion-cell lying under it. These pits are either simple, viz. with only an ‘olfactory rod’ (Tabanus, Fig. 283, and other Diptera, Vanessa), or compound (Muscidæ, and most other Diptera, and Philonthus). It is important that these pits are partly open (in the above-named groups of insects), and partly closed and covered with a thin membrane, under whose concavity the olfactory rods end (Orthoptera, Melolontha, and other lamellicorns). 3. Short, thick pits sunken slightly into the surface of the antennæ, and over this a chitinous peg perforated at the end, in whose base, from the interior, projects a very singular nerve-peg, which is situated over an olfactory ganglion-cell, and provided with a slender crown of little rods, and flanked on each side by a flagellum-cell (Hymenoptera). 4. Round or crevice-like pits covered over by a perforated chitinous membrane with nerve-rods like those in 3, but in place of the flagellum-cell with ‘membrane-forming’ cells spread before it. Hauser finally mentions further differences in the ganglion-cells sent out into the nerve-end apparatus. These exhibit in Diptera and Melolontha only one nucleus, in Hymenoptera a single very large one (with many nucleoli) and three small ones, in Vanessa six, in Orthoptera a very large number of nuclei, etc.”