96 INTERNAL ANATOMY OF INSECTS. 
rapid growth and transformations of the larva?, and the 
stationary existence of the imago, &c. Lastly he remarks, 
that the phenomena of this circulation do not throw 
any light on the obscure subject of the mode of nutrition 
in perfect insects ; which therefore must still be supposed 
to be effected according to the idea of Cuvier, without 
the intervention of vessels a . 
Whatever be the functions of the dorsal vessel, this 
seems the most proper place to state to you what further 
is known respecting it. Its construction is nearly alike 
in insects in all their states, except that in the imago it 
is shorter and narrower. Reaumur has affirmed, and 
before him Malpighi made a similar observation, that in 
chrysalises newly disclosed from the larva, and yet trans- 
parent, the motion of the included fluid is the reverse of 
what it has been in that state, it being propelled from 
the head to the tail, which he found to be the case also 
in the imago b . If this be true, and there is no reason to 
doubt his accuracy, when they are more advanced, it re- 
sumes its old course, as Lyonet observed, from the tail 
to the head c . But probably it is not always uniformly 
in the same direction, since Malpighi states that a very 
slight cause will change its course, and that the pulsa- 
tions differ in quickness in different portions of the heart d . 
If its course were really always the same, and in one di- 
rection, without any reflux, it would seem to follow that 
the fluid must be absorbed at one end, and, if there was 
no outlet, transpire at the other, which would be a kind 
of circulation. In Syrphus Pyrastri and other aphidi- 
3 Introd.to Comj). Anat. ii. 399—. Engl. Trans. 
b Reaum. i. 409, 643-. Malpigh. Be Bombyc. 38. 
c Lesser L. ii. 87 note *, d Ubi supra. 
