96 INTERNAL ANATOMY OF INSECTS, 



rapid growth and transformations of the larvae, and the 

 stationary existence of the imago, Sac. 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 aphid i- 



a Introd. to Comp. Anat. ii. 399. Engl. Trans. 

 b Reaum. i. 409, 643. Malpigh. De Bombyc. 38. 

 e Lesser L. ii. 87 note *. A Ubi supra. 



