190 MR. LUBBOCK ON THE CUTANEOUS MUSCLES 



manage pour faciliter rondoyement que fait Ic corps de la chenille quand elle marclie, et 

 qui en rend le mouvement progressif plus ais6 que s'il etoit vermiculaire." 



It is hardly necessary to say, that there is no similar muscle on the dorsal side in 

 Cossus or in Fygcera. 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. 



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 larvae, 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 diiferent 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 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 

 carried out with it a portion of the sternum of the first thoracic segment, in addition to 

 that belonging to the second maxillary segment, of which it normally consists. 



Dr. Ratzeburg was under the impression that the last segment of the head put on a 

 thoracic character in the larvse of certain Hymenoptera. Mr. Westwood, however, has 

 thrown great doubt upon this supposition, if indeed he has not disproved it altogether*. 



* See the Trans. Ent. Soc. toI. ii. p. 125, and Todd's Cyclopaedia, article Insecta, p. 871. 



