1887] MICROSCOPICAL JOURNAL. oT 
tebrates, they are very sluggish. It is hard to say what they feed on; 
apparently, not vegetable matter. As to size, they vary considerably ; some 
are comparatively minute. The largest known ( Collossendets gigas) has 
legs nearly 12 inches long, and a body less than 2 inches. It is doubtful if 
any are parasitic. See Mech. and World of Sct., 1886, p. 235. 
Morphology of the insect-wing. By N. Cholodkovsky, St. Petersburg.* 
Contrary to the text-book teaching on the subject, the first and second thoracic 
somites are not anchylosed in Lepidoptera. After carefully severing the pro- 
thorax and cleaning off the soft parts by means of caustic potash, the typical 
parts, notum, pleura and sternum, may be noted. On the border between the 
_feebly developed notum and pleura on each side is a pouch from the chitinized 
shell, which is not very noticeable. From its position and form this pouch is 
precisely like that on the second and third thoracic wings of most insects, so 
that one would scarcely err if he gave to this appendage the name of the 
rudimentary prothoracic wing. Such a prothoracic wing have I observed in 
many Lepidoptera of all the principal families; in some cases very small 
(Tineidz), in others nearly as large as the prothorax itself (Noctuide). 
The presence of such appendage has been observed in other insects. Fr. 
Miiller has reported a rudimentary prothoracic wing in Termite larve ; here 
in larva all three thoracic somites bear pouches, of which, later, the meso- and 
metathoracic ones persist and develop into wings, the prothoracic abort. 
Woodward} describes and figures a fossil insect whose prothorax bears two 
wing-like appendages. Gruber, in his work, Zhe /usects, vol. 1, 88, inclines 
to regard the side-flap of the prothorax of the locust as an undeveloped wing. 
The fact that the lepidoperous insect, while the most divergent of all the 
insects from the form of the prot-insect, should possess this ancestral character 
is remarkable, but accounted for upon the doctrine of reversion. 
_ The physiological réle of the rudimentary wing-sack is very difficult to 
imagine. It does not appear during the early larval life, but only during the 
chrysalis stage, at least such is the case in the form observed, Vanessa urtice ; 
but though the physiological réle of the part is uncertain, its morphological 
significance is very clear. After the works of Moseby and Balfour upon 
Peripatus, it is clear that the insects have sprung from aquatic forms. Such 
inference is strengthened by the presence in some imagines (e. @., Perlidz) of 
gill trachezee. It seems undoubted that insect-wings are especial appendages 
of the body which at first pertain to all segments of the thorax, but later 
survive only upon the two posterior segments. The first function of these 
wasrespiratory. When, later, some forms assumed an aquatic life, this structure 
developed further and became the gill trachee. But these sacs may occupy 
one of two positions, the one more ventral (the gill trachez of Perlidz), and 
the other more dorsal. The latter position is that of appendages homologous 
with the dorsal appendages of land hexapods, whereby the direct change 
in Epheminde of the gill trachez to wings is explained. In this way the 
improbable view of Gruber’s that they arise from two sorts of sac is rendered 
unnecessary. 
THE BYSSAL ORGAN IN LAMELLIBRANCHS.{—The first portion of Dr. Bar- 
rois’ article is a very full description of the byssal organs or its remains in 
forms from almost every family, twenty-one in all, and in forty-nine species 
of lamellibranchs. There is also a historical résumé of the subject, description 
of additional glands, and a discussion of the homologous organs in gasteropods. 
* Zool. Anz., p. 615, 1886. + Q. J. Geol. Soc., Lond., 32, 60-64, pl. 9, f. x. 
cs eon du Pied et les Pores @Aquiferes chez les Lamellibranches—Par le Dr. Ih. gee Lille, 1885, 
PP. 160, pl, x 
