13 15. J 0« tfie UiBi of the Dorsal Vessel, 87 1 



very well on a caleoptera lamellicornis. I removed with all pos- 

 jiblc care, in the ateuchus semi-punctatuSi the vesicular tracheae 

 which surround the dorsal vessel, as well as their ramifications. 

 When they were removed the concractions of the vessel diminished 

 by degrees. 1 had indeed removed some muscular fibres ; but in 

 so small a quantity, that I do not believe that cause had a remark- 

 able influence. These contractions have continually gone on di- 

 minishing, and the diminution was much greater than what is the 

 consequence of pain, and of the cessation of certain functions. 

 I believe, therefore, that the contractions of the dorsal vessel are 

 proportional to the quantity of adipose tissue ; the energy of the 

 inuscular fibres tliat surround it, and of the number of tracheae 

 Avhich enter into it, or of the air which it receives. 



Let us see now whether the nerves have not some influence on 

 these contractions, as the dorsal vessel receives a certain number of 

 them. 'Jo deternune this influence, 1 removed the spinal marrow 

 with the nerves coming from it, as far as I could distinguish them, 

 and then examining the contractions of the dorsal vessel, I could 

 not perceive that they were sensibly enfeebled. I repeated this 

 exj)eriment on a great number of individuals of different ordeis, 

 and I always obtained the same result. Hence 1 conclude, tliat 

 the nerves have no very sensible influence on the contractions of 

 the dorsal vessel. It is possible, that in all these animals in which 

 the nervous system is very much divided, and the principal centre 

 has little preponderance, the nervous influence is less distinct. 

 This 1 shall endeavour to determine by future researches. 



It remained still to determine whether the contraction of the 

 dorsal vessel does not depend in part on the circulation of the liquid 

 which it contains. We have already observed, and the observation, 

 since the time of Malpighi has been renewed by all anatomists, 

 that the humour of the dorsal vessel has a very irregular motion, 

 and that the fluid often appears to go from the head towards the 

 tail, and at other times to take a contrary direction. Sometimes 

 the dorsal vessel contracts at its two extremities, while these con- 

 tractions do not take place in tiie middle of the organ, especially if 

 the dorsal muscles have been removed in this part. So that the 

 liquid in the dorsal vessel appears at one time to move with extreme 

 rapidity, at another very slowly, without any apparent con- 

 nexion between this iiregularity and the state of the insect. But 

 how can this irregular motion be reconciled with the circulation of 

 a fluid analogous to the blood, and how can a circulation take place 

 without vessels? All these facts are in themselves so conclusive, 

 that it is diflicult to consider the dorsal vessel as a heart, and, of 

 course, to admit that the contractions arc produced by a liquid in 

 circulation. In the second place, if we pierce the heart of any 

 animal whatever, the moment the blood arrives it rushes out in a 

 quantity proportional to that which enters the heart. It was im- 

 portant, therefore, to determine whethor this would happen when 

 the dorsal vowel of inbtct'^ ii punctured. Tor that purpose \ cho'ie 



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