INTERNAL ANATOMY OF INSECTS. 83 
who injected it, regarded as a simple artery without strik- 
ing contractions? but to steer clear of any hypothesis, 
I shall merely call it the dorsal vessel (Pseudocardia). 
When carefully taken out of the body it is found to be 
a membranous tube closed at each end, in many larvee 
of equal diameter every where, but in perfect insects 
usually widest at the anal extremity‘, and attenuated into 
a very slender filament towards the head. In some in- 
sects, however, as in the larva of the chameleon-fly 
(Stratyomis Chameleon), it is attenuated at both ends, and 
in the Ephemera is alternately constricted and dilated as 
Malpighi describes that of the silk-worm 4, a dilated por- 
tion belonging to each segment®. 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 
Lyonnet denominates its wings‘, the action of which pro- 
duces its systole and diastole, and their propagation from 
the tail towards the head&. Under the last pair of these 
wings it is strengthened by a large number of circular 
muscular fibres’, I have stated it, with most writers, 
to be closed at each extremity; but from Lyonnet’s words 
it should seem that, in the Cossus, he considered it as 
open and expanded at its anterior end!. He seems also 
to suspect, that, by means of what he calls the frontal 
ganglions, a fluid is derived from the dorsal vessel to the 
@ Reaum. i. 160—. > Cuv. Anat. Comp. iv. 418. 
¢ Marcel de Serres Mem. du Mus. 1819. 69. 
@ Swamm. Bibi. Nat. t. xl. f. 4. t. xv. f. 4. 
© De Bombyc. t. ii. f. 4. * Ubi supr. 414. & Ibid. 425—. 
» Ibid. 419. i [bid. 412. 
Ge 
