348 On the Uses of the Dorsal Vessel. [Not. 



respecting which, notwithstanding the fine experiments of Lyonnet, 

 Swamrnerdam, Comparetti, and Cuvier, naturalists had not made 

 up their minds. The more progress we make in the details of the 

 organization of articulated animals, the more we see the justice of 

 the fine theorem explained by the illustrious author of the Compa- 

 rative Anatomy, that whenever the blood does not go in search of 

 air, the air must come in search of the blood. The insects are 

 undoubtedly the articulated animals that give the most evident 

 demonstration of this general law, as they are likewise the animals 

 in which air plays the greatest part. This fluid is spread through 

 them in so great quantity, that we may say with propriety that 

 every part of an insect breathes or enjoys the impression of the air, 

 that subtile fluid, which, according to the fine experiments of the 

 ancients, is as well the aliment of life as of flame. 



Insects appear at the head of articulated animals with respect to 

 the quantity of their respiration. They owe this advantage to the 

 absence of vessels destined to contain thejblood, and to the neces- 

 sity in which they are of having a circulation of air, since they 

 have no circulation of blood : but how the circulation of this 

 incompressible fluid is produced, and by what vessels his performed, 

 are questions which it is of importance to inquire into and decide. 

 It may take place in the same manner for those who respire air 

 unchanged as for those who separate it from water. Considered in 

 this point of view, our observations may have some interest. No 

 observer before us had described in a general manner, and with the 

 necessary details, the variations which the respiratory organs in that 

 order of animals experience, nor the differences observable in them 

 which depend upon the mode of respiration itself. We have not 

 been less careful in examining the other details of the organization. 

 The great number of observations which we have made on articu- 

 lated animals has demonstrated to us the influence which the heart 

 exerts over the absorbing system. Accordingly we have found the 

 chyliferous vessels follow in some measure the blood-vessels, and 

 never show themselves without the last, though in some eases they 

 disappear before them. This at least is what we have observed in 

 the arachnides, the last class of articulated animals, in which there 

 exists a heart and blood-vessels. This connection had been per- 

 ceived before. M. Cuvier, to whom anatomy owes such beautiful and 

 important discoveries, first pointed out the dependence which exists 

 between these two systems. 



Having acquired a knowledge of the organization of the prin- 

 cipal articulated animals, we were enabled to rise to general consi- 

 derations respecting the classification of the beings composing this 

 family. We particularly devoted our attention to the arachnides, 

 the animals of that kind the least circumscribed. We have endea- 

 voured to demonstrate that in a rigorous method of classification we 

 ought not to unite animals which have a heart and circumscribed 

 resphv.tory organs with those that have no heart and ramified respi- 

 ratory organs. Accordingly we have not adopted the class of 



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