8t 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 b , 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 ivi?igs 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 larva?. 
n Cuv. Anat. Comp. iv. 418. 
b Marcel de Serres Mem. du Mux. 1819. 69. 
e Swamm. Bibl. Nat. t. xl./. 4. t. xv.f. 4. 
d De Bombyc. t.m.f. 4. e Ubi sapr. 414. f Ibid. 425—. 
e Ibid. 419. h Ibid. 412. ' Lyonet Anat. 413. 
