190 , MR. LUBBOCK ON THE CUTANEOUS MUSCLES 
ménagé pour faciliter l'ondoyement que fait le corps: de la chenille quien elle marche, et 
qui en rend le mouvement progressif plus aisé que s’il étoit vermiculaire.” 
It is hardly necessary to say, that there is no similar muscle on the dorsal side in 
Cossus or in Pygæra. In Tipula, on the contrary, there is a dorsal muscle to which 
these remarks would well apply. . 
The great flexibility of the back shows itself, however, in many other ways. In Tipula 
there lie upon each side of the muscle 6, which is here represented by four distinct 
fascicles, five muscles, corresponding to 16, 17 and 18 on the ventral side; those on the 
other side being apparently a great development of 2, which becomes almost as important 
as 16, 17 and 18 together. Moreover, 1 and 21, instead of having their anterior termi- 
nations a little behind those of 16, 17 and 18, completely alternate with them; and, 
again, there are other muscles whose posterior insertions are close to those of 1 and 21, 
while they pass as far forwards as 2 on the one hand, and 16, 17 and 18 on the other. 
These arrangements must make the body much more supple. i 
Once more, there are strong oblique muscles both at the back and at the ventral side, 
which must give the animal great powers of twisting itself forward with a corkscrew-like 
motion. | 
I hope, however, at some future time to be able to lay before the Society a complete 
account of the muscles of these larvæ, which I have dissected and figured with great care, 
and shall content myself at present with mentioning one other remarkable peculiarity. 
The muscles of the first four body-segments are alike, and very different from those of 
the posterior somites; we must suppose, therefore, either that the thorax of insects has 
in reality four segments, or that the muscles of the first abdominal or last cephalic seg- 
ment have become developed like those of the thorax; in fact, that the first segment of 
the abdomen, or the last of the head, has detached itself from its usual position and 
joined itself to the thorax. 
The latter hypothesis seems to me more probable, and it is also supported by the position 
of the anterior ganglia, which are contained in the second segment (first body-segment) — 
and that of the labium, which also rises in this segment, although its upper surface has — 
partially coalesced with the under side of the head. I am reminded, however, by Prof. 
Huxley that neither of these conditions | 
is conclusive. The anterior abdominal ganglia 
not unfrequently move forwards into the 
not u thorax, so that the cephalic ganglia may perhaps 
in this case be moved back; and the labium, not being homologous with a pair of coalesced 
appendages, but simply a protrusion of the sternal surface, may perhaps in this case have 
SØR - with it a portion of the sternum of the first thoracic segment, in addition to 
Dr. mnd : € com øy Segment, of which it normally consists. 
thoraeie ER : = er the auiyression: that the last segment of the head put on à 
thrown td Tom arve of certain Hymenoptera. Mr. Westwood, however, bas _ 
wun great doubt upon this Supposition, if indeed he has not disproved it altogether*. . 
* See the Trans. i. 
8. Ent. Soc. vol. ii. p. 125, and Todd’s Cyclopædia, article Insecta, p. 871. 
