LITERATURE ON THE SPINNING GLANDS
Helm, E. Anatomische und histiologische Darstellung der Spinndrüsen der Schmetterlingsraupen. (Zeitschr. f. wissens. Zool., xxvi, 1876, pp. 434–469, 2 Taf.)
Lidth de Jeude, Th. W. van. Zur Anatomie und Physiologie der Spinndrüsen der Seidenraupe. (Zool. Anzeiger, 1878, pp. 100–102.)
Engelmann, W. Zur Anatomie und Physiologie der Spinndrüsen der Seidenraupe. (Onderz. Phys. Lab. Utrecht, iii, 1880, pp. 115–119.)
Joseph, G. Vorläufige Mitteilung über Innervation und Entwickelung der Spinnorgane bei Insekten. (Zool. Anzeiger, 1880, pp. 326–328.)
Poletajew, N. Ueber die Spinndrüsen der Blattwespen. (Zool. Anzeiger, 1885, pp. 22–23.)
Meinert, Fr. Contribution à l’anatomie des fourmilions. (Overs. Danske Vidensk. Selsk. Forh. Kjöbenhavn, 1889, pp. 43–66, 2 Pls.)
Blanc, Louis. Étude sur la sécrétion de la soie et la structure du brin et de la bave dans le Bombyx mori. Lyon, 1889, pp. 48, 4 Pls.
—— La tête du Bombyx mori à l’état larvaire. Anatomie et physiologie. (Extrait du volume des Travaux du Laboratoire d’Études de la Soie. Années 1889–1890, Lyon, 1891, pp. 180, 95 figs.)
Gilson, G. Recherches sur les cellules sécrétantes. La soie et les appareils séricigènes: I. Lépidoptères. (La Cellule, 1890, vi, pp. 115–182, 3 Pls. I, Lépidoptères (suite); II, Trichoptères. Ibid., x, pp. 71–93, 1893, 1 Pl.)
Garman, H. Silk-spinning dipterous larvæ (Science, xx, 1893, p. 215).
Also the writings of Meckel, Pictet, Duméril, Klapálek, Wistinghausen, Loew, Hagen, Fritz Müller, Kolbe, McLachlan, de Selys-Longchamps.
c. The cæcal appendages.
These diverticula of the mid-intestine (“stomach”) are appended to the anterior end, and in the living, transparent larva of Sciara, which has two large, long, slender cœca (Fig. 341), the partly digested food may be seen oscillating back and forth from the anterior end of the stomach into and out of the base of each cæcum. In the Locustidæ (Anabrus, Fig. 299) and Gryllidæ (Fig. 344, e) there are two large, short cæca, and in the locusts (Caloptenus) there are six cæca, while cockroaches have eight. In the Coleoptera (Carabidæ and Dyticidæ) these large cæca appear to be replaced by very numerous slender, minute villi or tubules, which arise from the anterior part of the stomach (Figs. 317, r, also 342).
These cæca differ in structure from the stomach, as shown by Graber, as well as by Plateau and by Minot. The latter states that a single transverse section of one of the diverticula of the locust demonstrates at once that its structure is entirely different from that of the stomach.
Fig. 341.—Larva of Sciara: s.gl, salivary gland; ur.t, urinary tubes; i intestine; st, stomach; cae cæcal appendages; t, testis.
Its inner surface is thrown up into longitudinal folds, generally twelve in number. These folds shine through the outer walls, and are accordingly indicated in the drawings of Dufour, Graber, and others. The entire cæcum has an external muscular envelope, outside of which are a few isolated longitudinal muscular bands. The folds within are formed mainly by the high cylindrical epithelium which lines the whole interior of the cavity. Tracheæ ramify throughout all the layers outside the epithelium. There are appearances of glandular follicles in the bottom of the spaces between the folds. (Minot.)
Burmeister supposed that these cæca were analogous to the pancreas, and this view has been confirmed by Hoppe Seyler, Krukenberg, Plateau, and others, who claim that the digestive properties of the fluid secreted in them agrees with the pancreatic fluid of vertebrates.
Fig. 342—Cross-section of mid-intestine of Acilius sulcatus, showing the arrangement of the cæca, two tracheæ passing into each cæcum.—After Plateau.
d. The excretory system (urinary or Malpighian tubes)
The excretory matters or waste products of the blood tissue of worms are carried out of the body by segmentally arranged tubes called nephridia. As a rule they arise in the blood sinuses of the body and open externally through minute openings in the skin. As there is a pair to each segment (in certain oligochete worms two or three pairs to a segment), they are often called segmental organs. In the annulate worms each segment of the body, even the cephalic or oral segment, originally contains a pair of these excretory organs. These vessels may have survived in myriopods and perhaps do exist in insects as urinary tubes, and also occur in many of the Arachnida, and thus are characteristic of each important class of land arthropods, but are either wanting or are very rudimentary or much modified in the marine classes, notably the Crustacea and Merostomata (Limulus), where they are represented by the shell-glands of Copepoda, green glands of the lobster, and the brick-red glands of Limulus.
Fig. 343.—Digestive canal of Perla maxima: l, upper lip; mh, buccal cavity; ap, common end of salivary ducts (ag); o, œsophagus; s, s, salivary glands, arranged segmentally; b, cæca of chyle-stomach; lg, their ligaments of attachment; mp, urinary tubes; r, rectum; af, anal orifice.—After Imhof, from Sharp.
In the earliest tracheate arthropod, Peripatus, these tubes are well developed and are highly characteristic, each segment behind the head bearing a pair (Fig. 4, so4-so9). It has been suggested by some, but not yet proved, that the urinary tubes of insects are morphologically the same as the segmental organs of worms and of Peripatus; but there are no facts directly supporting this view, and, as Sograff states, it is a pure hypothesis and can only be confirmed or disproved by very detailed researches on the development of the urinary tubes of myriopods and of insects. Others regard them as probably homologous with the tracheæ, since they have a similar origin. As, however, they arise in the embryo as outgrowths of the proctodæum they may have arisen in myriopods and insects independently, and not be vermian heirlooms.
While in worms and in Peripatus a pair of these segmental organs occur in each segment, in insects this serial arrangement is not apparent; those with a purely excretory function are not segmentally arranged, with outlets opening externally, but arise as outgrowths of the hind-intestine or proctodæum of the embryo, not being segmentally arranged. The place of their origin is usually the dividing line between the mid and hind intestine (Fig. 343, mp); this applies to Scolopendrella (Fig. 15, urt) as well as to insects.
The urinary tubes are usually long, slender, blind, tubular glands varying in number from two to over a hundred, which generally arise at the constriction between the mid and hind intestine, and which lie loosely in the cavity of the body, often extending towards the head, and then ending near the rectum (Figs. 301, 310, vm). They were first discovered by the Italian anatomist Malpighi, after whom they were called the Malpighian tubes. While at first generally regarded as “biliary” tubes, they are now universally considered to be exclusively excretory organs, corresponding to the kidneys of the higher animals.
Fig. 344.—Digestive canal and appendages of the mole-cricket; a, head: b, salivary glands and receptacle; c, lateral pouch; d, stomatogastric nerves; e, anterior lobes of stomach; f, peculiar organ; g, neck of stomach; h, plicate part of same; i, rectum; k, anal gland; m, urinary tubes.—After Dufour, from Sharp.
Usually arising from the anterior end of the hind-intestine where it passes into the mid-intestine, in certain forms they shift their position, in some Hemiptera (Lygæus, Cimex) opening into the rectum, while in the Psyllidæ they arise from the slender hinder part of the mid-intestine, being widely separated at their origin. (Fig. 321.)
The length varies in different groups; where they are few in number (two to four, six to eight), they are very long, but where very numerous they are often short, forming dense tufts, each tuft connecting with the intestine by a common duct (ureter), or, as in the mole-cricket, the numerous tubes empty into a single duct (Fig. 344); in the locusts (Acrydiidæ), however, they are arranged in 10 groups, each group consisting of about 15 tubes, making about 150 in all; and are much convoluted and wound irregularly around the digestive canal, and when stretched out being about as long as the entire body.
The urinary tubes occur in twos, or in multiples of two, though a remarkable exception is presented in the dipterous genera Culex and Psychodes, in which there are five tubes; the young and fully grown larvæ, as well as the pupa and imago of Culex, having this number (Fig. 433, mg.)
In many insects (Pentatoma, Cimex, Velia, Gerris, Haltica, Donacia, and often in caterpillars), the vessels open into a sort of urinary bladder connecting with the intestine on one side.
Fig. 345.—A, section of urinary tube of Periplaneta; B, part of tube of Perla; p, peritoneal membrane; c, cavity or lumen; n, nucleus of a secreting cell.—After Schindler.
In the larvæ of some insects the blind ends of the tubes are often externally bound to the rectum, in the silkworms being attached by fine threads to the intestine, while in some flies (Tipula and Ctenophora), two vessels may unite to form a loop. In all larval Cecidomyiæ, the two tubes are united to form a loop which curves backward, opening near the vent, the proctodæum being very short. (Giard.)
Fig. 346.—Portion of a urinary tube of Calliphora vomitoria: tr, trachea; l, lumen; k, nucleus.—After Gegenbaur.
While usually the urinary vessels form simple tubes, in many species of Lepidoptera and Diptera they are branched, thus resembling those of spiders and scorpions. Moreover, in many Lepidoptera and Diptera (Fig. 308), the tubes are not simple, but are lobulated, and in some Hemiptera (Pentatoma, Notonecta, and Tettigonia) are twisted or lace-like. In rare cases there are two kinds of urinary tubes; in Melolontha vulgaris, two of them are partly lobulated and yellow, while the other two are simple and white. Their color in beetles varies, some being whitish or yellowish; in Geotrupes, Dyticidæ, Hydrophilidæ, etc., reddish brown; in Gryllotalpa as well as Locusta viridissima, there are two different kinds of vessels, differing in contents and in color (white or yellow), as well as histologically. (Schindler.)
The exterior of the tubes is richly provided with tracheæ, which often form a web around them, and the fine branches often seem to attach them to the intestine. In Acheta they are enveloped by a very delicate, loose network of muscular fibres. (Schindler.)
The urinary tubes consist, according to Schindler, of at least three cellular layers (Fig. 345):—
1. An external, connective, nucleated membrane, the peritoneal membrane.
2. A very delicate homogeneous basal membrane, the tunica propria.
3. A single layer of large polygonal excretory cells.
4. Lining the internal canal a chitinous layer penetrated by pore-canals, the intima often wanting.
The secretory cells are usually of the same size, but in many cases are relatively small; sometimes four to six or more form the periphery of the canal, sometimes three or only two. In some insects the cells are so very large that a single cell forms the entire periphery. The nuclei in the Lepidoptera (Papilio, Pontia, Cossus) are large and irregularly branched.
The excretions of the Malpighian vessels, derived from the blood and from the fat-body, are more or less fluid and granular, sometimes pulpy. From the cells they pass into the canal, thence into the intestine, and thence out of the body. How, says Kolbe, the secretion passes into the intestine, whether by the contraction of the fine fibrillæ of the peritoneal membrane, or by the external pressure of the other organs, or by the pressure of the secretory matter behind, is not yet known. Grandis observed in living Hydrophilus that the urinary tubes moved, without the muscles seeming to show what caused the motion. Moreover, the cells incessantly changed their form. At a lower temperature such motions ceased. The tracheæ, ending freely in the cells, did not anastomose. (Kolbe.)
The different colors of the tubes (white, yellow, red, brown, or green) is due to the hue of the excretions, and is independent of the color of the blood and of the urinary substances held in the secreted matter.
Schindler found that insects of different stages, collected in winter, differed very much in their urinary secretions, the tubes in the adults being entirely empty, while in the larvæ they were filled full, so that he concluded that in the former the process of excretion during the winter hibernation is very slow, but in the latter very rapid.
As to the activity of the urinary vessels the following experiments will throw some light. Tursini fed a Pimelia with fuchsin; its urinary tubes were consequently colored red. Schindler fed insects with indigo-carmine, which was excreted by the urinary tubes; Kowalevsky arrived at the same results, which seems to prove that these vessels are analogous to the kidneys of vertebrates. Moreover, Schindler injected through the side of the first abdominal segment into the cavity of the body of a Gryllotalpa a concentrated solution of sodium salt of indigotin-disulphonic acid. After one or two hours the external portion of the epithelium of the urinary vessels was stained deep blue, while the inner portion remained of the normal transparency; the nuclei being for the most part deeply stained. Between one and two days after, the staining matter had not yet wholly passed through the central canal, the surface recently stained still appearing light blue.
The solid contents of the urinary tubes consist partly of crystals, which occur singly in the epithelial cells, or form scattered masses when situated in the central canal. Besides tabular rhombic crystals, there occur concretions which contain uric acid, and probably consist of urate of soda, also octahedral crystals of chloride of soda, and quadro-pyramidal crystals of oxalate of lime. Also acicular prisms occur; besides chloride of soda, phosphates, carbonate of lime, oxalate of lime in quantity, leucine, coloring matters, etc.; while the fluid secretion also contains urea (?), uric acid, and abundant urates; uric acid crystals were precipitated by the addition of acetic acid, and by adding hydrochloric acid crystals belonging to the dimetric system were formed. The often numerous spheroidal small granules are biurate of soda and biurate of ammonia. Pale, concentrically banded concretions are leucine pellets.
According to Kölliker the contents of the urinary vessels[[55]] in general are: (1) round granules of urate of soda and urate of ammonia; (2) oxalate of lime; and (3) pale transparent concretions of leucine. Crystals of taurin are also said to occur. (Claus’ Zoölogy, p. 531.)
Although uric acid is characteristic of the urinary tubes, yet sometimes it is wanting in them, while uric acid substances in quantity occur in the fat-body or in the mid-intestine.
In the living insect the urinary tubes remove urates from the blood; “the salts are condensed and crystallized in the epithelial cells, by whose dehiscence they pass into the central canals of the tubules and thence into the intestine.” (Miall and Denny.)
The process of excretion is carried on not only by the urinary tubes, but also, as Cuénot has recently shown (1896) in Orthoptera, by the pericardial cells and certain cells of the fat-bodies. In the last-named cells urates are stored throughout life; the pericardial cells apparently secrete but do not store waste products, which are finally eliminated by the urinary tubes, the latter constantly eliminating waste.
Primitive number of tubes.—Wheeler considers the primitive number of urinary tubules to be six, other authors regarding two pairs as the primary or typical number; and while Wheeler agrees that the more ancestral tracheate arthropods had but a single pair, Cholodkowsky supposes the primitive number in insects themselves to be a single pair. This view is strengthened by the fact that Scolopendrella has but a single pair (Fig. 15).
While Peripatus has no urinary tubes, in Myriopods a single pair arises, as in insects, from the hind-intestine.
Fig. 347.—Section of proctodæum of embryo locust, showing origin of urinary tubes (ur.t); ep, epithelial or glandular layer; m, cells of outer or muscular layer; a, section of a tube.
When in insects the number of these tubes is few, they are, with rare exceptions, arranged in pairs, so that Gegenbaur and others have considered this paired arrangement as the primitive one. When the tubules are very numerous in the adult, as in Orthoptera, the embryos and larvæ have a much smaller number, Wheeler stating that “in no insect embryo have more than three pairs of these vessels been found.” We have observed 10 primary tubes in the embryo of Melanopus (Fig. 347), from each of which afterwards arise 15 secondary tubules. In the Termites, only, do the young forms have more urinary tubes than the adults.
In Campodea there are about 16 urinary tubes and in Machilis either 12 (Grassi) or 20 (Oudemans); but in other Thysanura the number is much less, Lepisma having either four, six, or eight, according to different authors, and both Nicoletia and Lepismina having six, opening separately into the hind-intestine. On the other hand, these organs have not yet been detected in Japyx. Whether they exist at all in the Collembola, which are degenerate forms, is doubtful. The weight of opinion denies their existence, though they may yet be found existing in a vestigial condition. They are said by Tullberg and by Sommer to exist in Podura, but are of peculiar shape.
Coming now to the winged insects, in what on the whole is perhaps the lowest or most generalized order, the Dermaptera, the number is over 30, and their insertions regularly encircle the intestine. (Schindler.) In the most ancient and generalized family of Orthoptera, the Blattidæ, Schindler detected from 60 to 70 tubes, but in a nymph of Periplaneta not quite 10 mm. in length he found from 16 to 18, and in nymphs 4 to 5 mm. long there were only eight vessels; while Wheeler has found in the embryo of Phyllodromia germanica but four tubes. In the adult Acrydiidæ there are as many as 150, in the Locustidæ between 40 and 50, and in the Gryllidæ about 100.
The Ephemeridæ with about 40, the Odonata with 50 to 60 tubules, the Perlidæ with from 50 to 60, are polynephrious; while the Termitidæ and Psocidæ are oligonephrious, the former having from six to eight and the Psocidæ only four tubes. So also all the other orders not mentioned, except the Hymenoptera, have few of these tubes. The Hemiptera, with none in Aphidæ, a single pair in the Coccidæ, and two in all the rest of the order, have the fewest number.
In the Neuroptera there are from six to eight, while in a larva, possibly that of Chauliodes, Wheeler finds the exceptional number of seven.
The closely allied order Mecoptera (Panorpidæ), and also the Trichoptera, agree with the Neuroptera (Sialis) in having six. According to Cholodkowsky all Lepidoptera have six of these vessels, except Galleria, which has but four. He finds that in Tinea biselliella (also T. pellionella and Blabophanes rusticella) the larva has six vessels, which, however, undergo histolysis during pupation, a single pair arising in their stead. On this account he regards the primitive number of urinary tubes as two, or a single pair, this return from six vessels in the larva to two in the imago being considered a case of atavism.
In the Coleoptera, the number of urinary tubes is from four to six; in what few embryo beetles have been examined (Doryphora, Melolontha), there are six vessels, but in the embryo of Dyticus fasciventris, Wheeler has detected only four, this number being retained in the adult. He thinks that in beetles in general, a pair of vessels must be “suppressed during post-embryonic development, presumably in early larval life.”
In Diptera and Siphonaptera, the number four is very constant, there being, however, a fifth one in Culex and Psychoda (Fig. 400.)
The number of these vessels is very inconstant in the Hymenoptera, varying from six (Tomognathus, an ant, worker) to 12 (Myrmica), and in Apis reaching the number of 150.
In the embryo of the honey-bee and wall-bee (Chalicodoma), there are only four; we still lack any knowledge of the number in embryo saw-flies.
The following is a tabular view of insects with few urinary tubes (Oligonephria) and many (Polynephria). It will be seen that the number has little relation to the classification or phylogeny, insects so distantly related as the Orthoptera and Hymenoptera being polynephrious:—
Oligonephria
Collembola, 2 (Podura), Tullberg and also Sommer.
Thysanura, 4 (Lepisma); in Campodea, 16; in Machilis, 12 or 20; wanting in Japyx.
Psocidæ, 4.
Termitidæ, 6 (many in the young, Rathke).
Mallophaga, 4.
Physapoda, 4.
Hemiptera, 2 (Coccidæ, none in Aphidæ).
Neuroptera, 6–8. (In Sialidæ and Rhaphididæ 6; in Myrmeleonidæ and Hemerobiidæ, 8).
Trichoptera, 6.
Mecoptera, 6.
Lepidoptera, 2–4–6 (2 in Tinea, Tineola, and Blabophanes; in Pterophorus and Yponomeuta, 4).
Coleoptera, 4–6; never more.
4
Carabidæ,
Dyticidæ,
Staphylinidæ,
Gyrinidæ,
Palpicornes,
Lamellicornes,
Cantharidæ,
Buprestidæ
(in larva, 6; in beetle, 4).
6
Byrrhidæ,
Nitidulidæ,
Dermestidæ,
Cleridæ,
Meloidæ,
Pyrochroidæ,
Bruchidæ,
Bostricidæ,
Cerambycidæ
Chrysomelidæ,
Coccinellidæ.
Diptera, branching into 4 (Gegenbaur); in Culicidæ, and Psychoda, 5.
Siphonaptera, 4.
Polynephria
Orthoptera, 100–150. (In embryo Blattids, 4; in embryo locust, 10; in nymph of Gryllotalpa, 4.)
Dermaptera, “over 30” (Schindler).
Perlidae, 50–60.
Plectoptera (Ephemeridæ), 40.
Odonata, 50–60.
Hymenoptera, 20–150. (In embryo bees only 4; Cynipidæ, Ichnenumonidæ, and Formicidæ have the smallest number, 6–12.)
Here should be mentioned the singular fact discovered by Koulaguine that in the larva of Microgaster, the urinary tubes have no connection with the intestine, but open dorsally on the outside of the body on each side of the anus. Ratzeburg had stated that the last segment of the body was in the form of a vesicle. Koulaguine now shows that this vesicle is in reality the end of the intestine opening upwards; as the result of this dorsal opening of the intestine the Malpighian vessels open on the sides of the oval vent, and have no connection with the intestinal canal. Whether this is of morphological import, or is only a secondary adaptation, Koulaguine does not state, his paper being a preliminary abstract.
Wheeler thus sums up our present knowledge regarding the number and homologies of the Malpighian or urinary tubes:
1. It is very probable that the so-called Malpighian vessels of Crustacea and Arachnida are not the homologues of the vasa Malpighi of the Eutracheata (insects and myriopods).
2. The Malpighian vessels of the Eutracheata arise as paired diverticula of the hind-gut and are, therefore, ectodermal.
3. In no insect embryo are more than six vessels known to occur; although frequently only four are developed.
4. The number six occurs either during embryonic or post-embryonic life in members of the following groups: Apterygota, Orthoptera, Corrodentia; Neuroptera, Panorpata, Trichoptera, Coleoptera, Lepidoptera, and Hymenoptera.
5. The number four seems to be typical for the Corrodentia, Thysanoptera, Aphaniptera, Rhynchota, Diptera, and Hymenoptera.
6. The embryonic number in Dermaptera, Ephemeridea, Plecoptera, and Odonata has not been ascertained, but will probably be found to be either four or six.
7. There is evidence that in at least one case (Melolontha), the tetranephric is ontogenetically derived from the hexanephric condition by the suppression of one pair of tubules.
8. It is probable that the insects which never develop more than four Malpighian vessels have lost a pair during their phylogeny.
9. The post-embryonic increase in the number of Malpighian vessels in some orders (Orthoptera, Odonata, Hymenoptera) is secondary and has apparently arisen to supply a demand for greater excreting surface.[[56]]