LITERATURE OF THE ORGANS OF SMELL
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—— Contemplation de la nature, Ch. iii, p. 18.
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Leydig, F. Zum feineren Bau der Arthropoden. (Müller’s Archiv, 1855, pp. 376–480); Lehrbuch der Histologie, 1857, p. 220; Zur Anatomie der Insekten (Archiv für Anatomie, 1859, pp. 35–89 and 149–183).
—— Ueber Geruchs- und Gehörorgane der Krebse und Insekten. (Archiv f. Anat. u. Phys., 1860.)
—— Die Hautsinnesorgane der Arthropoden. (Zool. Anzeiger, 1886, pp. 284–291, 308–314, 265–314.)
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Troschel, H. Ueber das Geruchsorgan der Gliedertiere. (Verhandl. d. naturhist. Vereins d. preuss. Rheinlande u. Westfal., xxvii Jahrg., 1870, pp. 160–161.)
Packard, A. S. The caudal styles of insects sense-organs, i.e., abdominal antennæ. (Amer. Naturalist, 1870, pp. 620, 621. Also Proc. Bost. Soc. Nat. Hist., 1868, xi, p. 398.)
Paasch, A. Von den Sinnesorganen der Insekten im Allgemeinen, von Gehörund Geruchsorganen im Besondern. (Archiv für Naturgesch., xxxix Jahrg., i, 1873, pp. 248–275.)
Chadima, Jos. Ueber die von Leydig als Geruchsorgane bezeichneten Bildungen bei den Arthropoden. (Mitteil. d. naturwiss. Ver. f. Steiermark, 1873, pp. 36–44.)
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—— Études myrmécologiques en 1884, avec une description des organes sensoriels des antennes. (Bull. Soc. Vaud. sc. nat., 1885, Sér. 2, xx, pp. 316–380.)
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—— Neue Versuche über die Functionen der Insektenfühler. (Biol. Centralb., vii, 1887, pp. 13–19.)
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Mayer, P. Sopra certi organi di senso nelle antenne dei Ditteri. (Atti R. Accad. d. Lincei, Roma, Ser. 3, Mem. Cl. sc. fis., mat. e natur., iii, 1879, p. 11.)
Hauser, Gustav. Physiologische und histiologische Untersuchungen über das Geruchsorgan der Insekten. (Zeitschr. f. wissens. Zool., xxxiv, 1880, pp. 367–403, 3 Taf.)
Kraepelin, Karl. Ueber die Geruchsorgane der Gliedertiere (Oster-Programm der Realschule des Johanneums. Hamburg, 1883, pp. 48, 3 Taf.)
Schiemenz, Paulus. Ueber das Herkommen des Futtersaftes und die Speicheldrüsen der Bienen nebst einem Anhange über das Riechorgan. (Zeitschr. f. wissens. Zool., xxxviii, pp. 71–135, 3 Taf.)
Plateau, F. Expériences sur le rôle des palpes chez les arthropodes maxillés, I., Palpes des insectes broyeurs. (Bull. Soc. Zool. France, x, 1885, pp. 67–90.)
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Lubbock, J. On some points in the anatomy of ants. (Monthly Micr. Journ., 1887, pp. 121–142.)
Ruland, Franz. Beiträge zur Kenntniss der antennalen Sinnesorgane der Insekten. Diss. Marburg, 1888, p. 31, 1 Taf.
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With the writings of Baster, Lamarck, Cuvier, Treviranus, Oken, Lefebure, Duméril, Schelver, Bousdorf, Rosenthal, Burmeister, Slater, Balbiani, Marcel de Serres, Garnier, Berté, Porter, Sazepin, Reuter, Pierret, Duponchel, Driesch, Küster, Peckham, Lubbock, A. Dohrn, Lespès.
c. The organs of taste
The gustatory organs of insects are microscopic pits or setae, either hair-like or resembling short pegs, which form the ends of ganglionated nerves. They are difficult to distinguish morphologically from certain olfactory structures, and it is owing to their position at or very near the mouth that they are supposed to be gustatory in nature.
Meinert was the first (1860) to suggest that organs of taste occurred in ants. He observed in the maxillæ, and tongue of these insects a series of canals in the cuticula of these organs connected with ganglion-cells, and through them with the nerves, and queried whether they were not organs of taste. Forel afterwards (1874) confirmed these observations. Wolff in an elaborate work (1875) described a group of minute pits (Fig. 284) at the base of the tongue of the honey bee, which he supposed to possess the sense of smell, but Forel and also Lubbock attributed to these sensory pits the function of taste. Ten years afterward Will showed conclusively, both by anatomical studies and by experiments, that Diptera and Hymenoptera possess gustatory organs. He, however, denied that the organs of Wolff were gustatory, and maintained that organs of smell were confined to the maxillæ, paraglossæ, and tongue. As we shall see, however, what appear to be with little doubt taste-pits, with hairs or pegs arising from them, are most numerous on the epipharynx of nearly all insects, and situated at a point where they necessarily must come in contact with the food as it enters the mouth and passes down the throat.
Fig. 284.—Taste-pits on the epipharynx (C) of the honey-bee: B, horny ridge; R, R, taste-pits; L, A, A, muscular fibres; S, S′, a b c d e f, section of skin of œsophagus.—After Wolff.
Fig. 285.—Tip of the proboscis of the honey bee, × 140: L, terminal button or ladle: Gs taste-hairs; Sh, guard-hairs; Hb, hooked hairs.—After Will.
Kraepelin (1883) discovered taste-organs on the proboscis of the fly, and taste-hairs at the end of the tongue of the humble-bee (Fig. 285), and afterwards Lubbock critically discussed the subject, and concluded that the organs of taste in insects are situated “either in the mouth itself, or on the organs immediately surrounding it.”
Structure of the taste-organs.—The organs have been best studied by Will, who, besides describing and figuring the chitinous structures, such as the pits or cups, hairs and the pegs, showed that they were the terminations of ganglionated nerves.
Figure 286 represents the taste-cups on the maxilla of a wasp, and Fig. 287 the taste-cone or peg projecting from the cup or pit. The cell out of which the pit and projecting hair or peg are formed is a modified hypodermis cell; and the seta is apparently a modification of a tactile hair, situated at the end of a nerve, which just beneath the chitinous structures passes into a ganglion-cell, which sends off a nerve-fibre to the main nerve.
Will detected on the tongue of the yellow ant (Lasius flavus) from 20 to 24, and in Atta from 40 to 52, of these structures. The number of pits on the maxillæ vary much, not always being the same on the two sides of the same insect. We have observed these taste-cups in the honey and humble bee, not only at the base of the second maxillæ (Fig. 288, g), but also on the paraglossæ (pg).
Distribution in other orders of insects.—The writer has detected these taste-cups in other orders than Diptera and Hymenoptera. They very generally occur in mandibulate insects on the more exposed surface of the epipharynx (compare pp. 43–46). We have not observed them in the Synaptera (Lepisma and Machilis).
In the Dermaptera the taste-cups appear to be undeveloped in the nymph, while in the adult they are fewer in number than in any other pterygote order yet investigated.
In a species of Forficula from Cordova, Mexico, the taste-pits are few in number, there being only about a dozen on each side in all; most of them being situated on the anterior half, and a few near the base. The taste-pits are provided each with a short fine seta, as usual arising from the centre.
Fig. 286.—Under side of left maxilla of Vespa: Gm, taste-cups; Shm, protecting hairs; Tb, tactile hairs; Mt, base of maxillary palpus.—After Will.
In the order Platyptera (including Perla, Pteronarcys, Psocus, Termes, Eutermes, and Termopsis) we have been unable to detect any organs of taste.
Fig. 287.—Section through a taste-cup: SK, supporting cone; N, nerve; SZ, sense-cell.—After Will. This and Figs. 284–286 from Lubbock.
Fig. 288.—Tongue of worker honey-bee: pg, paraglossæ; B, the same enlarged, showing the taste-papillæ; C, D, base of a labial palpus (mx.′p) with the taste-papillæ; E, taste-cups on paraglossæ of Bombus; F, group of same on left, G, on right side, at base of labial palpus.
In the Odonata, however, they are fairly well developed; in Calopteryx, about 50 taste-cups were discovered; in a species of Diplax about 28, there being a group of 14 at the base of the epipharynx on each side of the median line, while in Æschna heros there are two groups of from 25 to 30 taste-cups, situated as in the two aforenamed genera.
In the Orthoptera the gustatory cups are numerous, well developed, and present in all the families except the Phasmidæ, where, however, they may yet be found to occur.
In a large cockroach (Blabera) from Cuba they are well developed. On each side of the middle of the epipharynx is a curved row of stiff, defensive spines, and at the distal end of each row is a sensory field, containing 20 taste-cups on one side and 23 on the other. Near the front edge of the clypeal region are two more sensory fields, situated on each side of the median line, there being 35 taste-cups in each field. The taste-cups in this form are rather smaller than usual in the order.
In the Acrydiidæ they are more numerous than in the Blattidæ. For example, in Camnula pellucida, near what corresponds to the front edge of the clypeus are two gustatory fields, each bearing about 35 taste-pits. Just in front, under the clypeo-labral suture, are two similar fields, each containing from 40 to 42 taste-pits. There are none in front of these. There are thus about 140–150 sense-cups in all.
The members of the Locustidæ (Fig. 26) appear to be better provided with the organs of taste than any other Orthoptera, those of the katydid numbering from 170 to 180. There are from 50 to 60 taste-cups in the front region; behind the middle a group of 25 on each side, and over an area corresponding to the base of the labrum and front edge of the clypeus is a sensory field with about 70 taste-cups on each side. They are true cups or beaker-like papillæ, some with a fine, others with a short, stout, conical seta.
The gustatory organs in the cave cricket (Hadenœcus subterraneus, Fig. 27), from Mammoth Cave, are highly developed, being rounded papillæ with the nucleus at the top or end. They are grouped on each side of the middle near the front edge, there being 25 on each side. An irregular row of these beaker-like organs extends along each side; some occur under the base of the labrum, but they are most numerous in a field corresponding to the front edge of the clypeus, there being 50 on each side, or 100 in all, where in Ceuthophilus there are only 9 or 10. It would thus appear as if the sense of taste were much more acute in the cave-dweller than in the out-of-doors form.
In the Coleoptera taste-cups and setæ are very generally distributed, though we were unable to detect them in Dendroctonus or in Lucanus dama. As seen in Fig. 57, we have observed numerous taste-pegs along the maxilla of Nemognatha lurida, but otherwise taste-organs have only been detected in the epipharynx. They not only occur in the adult beetles, but we have found them in the larvæ of cerambycid, scarabæid, and other beetles. In the adults taste-cups appear to be about as well developed in the carnivorous forms (Carabidæ) as in the phytophagous or lignivorous groups.
In Chlænius tomentosus there are about half as many of these organs as in Harpalus, while in Calosoma there are 90 taste-cups, 45 on each side, under the base of the labrum. The cups are papilliform, being rather high, with a seta arising from each.
In the Cicindelidæ, the epipharynx bears a sensory field quite different from that of the Carabidæ. There are no normal taste-cups, except a few situated on two large, round, raised areas which are guarded in front by a few very long setæ. On the surface of each area are numerous very long setæ which may, if not tactile, have some other sense, as they arise from cup-like bases or cells. Those on the outside are like true taste-cups, with a bristle but little larger than normal in taste-cups generally. We are disposed to regard this sensory field as a highly specialized gustatory apparatus.
In the Dyticidæ the taste-cups are nearly as described in the Carabidæ.
The Staphylinidæ are not well provided with taste-organs. Under the clypeus of Staphylinus violaceus, on each side near the middle, is a bare rounded area, in which are situated 4 or 5 papilliform taste-cups, and at the base behind them is another linear group of about 7 slenderer, somewhat curved, taste-cups. In the Elateridæ these organs are scantily developed.
In the Buprestidæ (Buprestis maculiventris alone examined) no true taste-cups were detected. On the other hand, the Lampyridæ are well supplied with them. Under the clypeus is situated a sensory field bearing 26 taste-cups, which are rather smaller than usual. Over the epipharyngeal surface are scattered a few taste-cups, but they are small and perhaps not gustatory. Under the clypeus of Lucidota punctata Lec. is a group of 12 taste-cups, and in the middle region of the epipharynx, situated in a field extending from near the base to near the front edge, are about 40 taste-cups, which, however, are not, as is usual, arranged on each side of the median line, but are scattered among the hairs of the pilose surface of the epipharynx. In the Cleridæ the taste-cups are few in number.
In the great family of Scarabæidæ, the presence of gustatory organs is variable. None occur in Lucanus dama, though in the June beetle (Lachnosterna fusca Fröhl.) they are abundantly developed. The epipharynx bears on each side outside of a spiny area a group of about 50 taste-cups, each bearing a long seta, those on the outside of the area passing into a few high, rather slender, papillæ, without a seta. On the under side of the clypeus is a median group of 10 taste-cups of singular form, the cups being large, with broad bases, which posteriorly bear three spines, of which the median one is the largest.
Taste-cups occur without any known exception in the longicorn beetles. In Leptura canadensis they are numerous; in Euryptera lateralis they are abundant along and near the middle of the anterior half of the labral region, and in Cyllene robiniæ Forst. (or pictus Drury) they are more numerous than usual, extending in an unbroken sensory field from near the front margin of the clypeal region to near the front edge of the epipharynx. The cups vary much in size, some being one-half as large as others; and those on the sides of the sensory field bear short, and a few others rather long, bristles, showing that the taste-cups are modified tactile bristles.
The Tenebrionidæ are fairly well endowed with taste-cups, their number in Eleodes obsoleta Say amounting to 30 or 40.
Those of the Meloidæ especially are unusual in size and number.
Fig. 289.—Epipharynx (ep) of Nemognatha: cl, clypeus; gh, gathering hairs; tc, triangular sensory field dotted with taste cups; A, the field enlarged.
In Nemognatha lurida Lec. (Fig. 289) the front edge of the epipharynx contains about 80 remarkably small taste-cups, arranged irregularly in a triangular sensory space, and not more than ¼ to ⅙, as large as those on the maxillæ of the same beetle. Unless the former structures are gustatory it is difficult to account for their presence here, and it will be observed that the taste-cups in Epicauta are unusually abundant. Thus in the middle and near the front of the epipharynx of the blister-beetle over 100 gustatory cups were counted. They are conical, papilliform, and truncated at the end as if open, the edge of the opening being ragged, though bearing no bristle, except in a few cases. Around the edge of the sinus, on the under side of the labrum, is a regular marginal row of large, longer, more distinctly chitinized taste-cups, whose walls are streaked up and down by chitinous thickenings. In E. callosa Lec. there are about 55 taste-cups under the labrum, besides about 10 cells, which may be gustatory structures, situated on either side of a median setose ridge which passes back under the clypeal region.
The taste-cups of the leaf-beetles are fairly numerous, judging from an examination of Diabrotica vittata. The surface of the epipharynx is pilose, but the median region is naked, and on the anterior half bears from 11 to 12 taste-cups, arranged each side of the median line in a rude Y. On each side, at the base of the labial region, are two sensitive fields, each bearing about 25 to 26 taste-cups. More were seen under the clypeus.
In the Neuroptera unmistakable taste-cups are not always present. In Sialis infumata along the median line of the epipharynx and near the front are about 20 scattered gustatory pegs, which are minute, but longer and more acute than usual. In Chauliodes maculatus there are one or two taste-cups under the front edge of the clypeus; others are scattered along the middle from the base of the labrum to the front, but are not arranged in definite order. In Corydalis cornutus no sense-cups, pits, or rods are present. In Chrysopa there are scattered cups armed with a short acute bristle, which are possibly gustatory in function. In Myrmeleon diversum also the presence of sense-pits or of taste-cups is doubtful, though a group of about 12 pits on each side of the clypeal region of the epipharynx, and a few situated at the base of the labral region, may be endowed with the sense of taste. In Mantispa brunnea, however, along the middle of the epipharynx are scattered about 30 unmistakable taste-cups, each bearing a short, fine hair.
In the Mecoptera (Panorpa debilis?) taste-cups, giving rise to a minute hair, occur on the labium in two regions, and also on the maxillæ situated on the stipes near the base of the palpi, and on the lacinia and galea. They are also to be found on the maxillæ of Boreus californicus, but were not detected on the labium.
They were first detected by Reuter in various microlepidoptera, and occur on the “basal spot” of the palpi of many butterflies. In a Tineid moth (Coleophora coruscipennella) we have detected what we suppose to be a group of four taste-pits on the inner side of the basal joint of the labial palpi.
Experimental proof.—No one, says Lubbock, who has ever watched a bee or wasp can entertain the slightest doubt as to their possession of the sense of taste. “Forel mixed morphine and strychnine with some honey, which he offered to his ants. Their antennæ gave them no warning. The smell of the honey attracted them, and they began to feed; but the moment the honey touched their lips they perceived the fraud.”
Will at first fed wasps with sugar, so that they frequently visited it; afterwards he substituted alum for the sugar. Eagerly flying to it, they had scarcely touched it when they drew back from the distasteful substance with the most comical gestures, and cleaned their tongues by frequently running them in and out, repeatedly stroking them with their fore feet. He noticed a great repugnance to quinine in nearly all the insects experimented on. Bees and wasps were observed to have a more delicate gustatory sense than flies, etc., which are more omnivorous in their tastes.