8i INTERNAL ANATOMY OF INSECTS. 



at each end % in many larvae of equal diameter every 

 where, but in perfect insects usually widest at the anal 

 extremity 5 , and attenuated into a very slender filament 

 towards the head. In some insects, however, as in the 

 larva of the chamaeleon-fly (Stratyomis Chamceleon\ it is 

 attenuated at both ends, and in the Ephemera is alter- 

 nately constricted and dilated as Malpighi describes that 

 of the silkworm , a dilated portion belonging to each 

 segment d . In the Cossus, and probably others, after the 

 third segment, it is furnished with nine pair, the three 

 posterior pair being the largest, of triangular transverse 

 bundles of muscular fibres, which Lyonet denominates 

 its wings e , the action of which produces its systole and 

 diastole, and their propagation from the tail towards the 

 head f . Under the last pair of these wings it is strength- 

 ened by a large number of circular muscular fibres &. 

 I have stated it as appearing to be closed at each ex- 

 tremity, because Cuvier and most writers have so re- 

 garded it, and probably it is so closed in the perfect in- 

 sect ; but from Lyonet's words it should seem that, in 

 the larva of the Cossus, he considered it as open and 

 expanded at its anterior end h . He seems also to sus- 

 pect, that, by means of what he calls the frontal gan- 

 glions, a fluid is derived from the dorsal vessel to the 

 spinal marrow. He likewise describes a large nerve as 

 passing through it and becoming recurrent '. Carus, as 

 we shall soon see, has also proved that this tube is not 

 closed in larvae. 



3 Cuv. Anat. Comp. iv. 418. 



b Marcel de Serres Mem. du Mus. 1819. 69. 



c Swamm. Bibl. Nat. t. xl./. 4. t. xv./. 4. 



d De Bvmbyc. t. iii./. 4. Ubi supr. 414. f Ibid. 425. 



& Ibid. 419. h Ibid. 412. z Lyonet Anat. 413. 



