1814.] On the Uses of the Dorsal Vessel. 351 



3. It was no less essential to ascertain if the contractions and 

 dilatations of the dorsal vessel were owing to the action o ithe fluid 

 contained in it. On this supposition it would be necessary to show 

 a kind of circulation of this fluid : while according to the other 

 hypothesis it became necessary to show that these contractions and 

 dilatations were not produced by the humor contained in the dorsal 

 vessel, but might be stopped without altering that vessel. 



■4. The organs of circulation appearing always to bear a relation 

 to the organs of respiration, it was necessary to examine if the 

 dorsal vessel was formed in the same manner in the species which 

 respire air directly, and in those which respire it contained in water, 

 or which decompose that liquid. 



5. All these researches ought necessarily to enable us to deter- 

 mine the influence of the organs of respiration on those of cir- 

 culation. If the influence of the first were demonstrated to act 

 completely on the second, we ought to observe that, in proportion 

 as the organs of respiration concentrate, or to speak more correctly, 

 cease to ramify, the organs of circulation will exhibit ramifications, 

 since the air going no longer in search of the blood it is necessary 

 that the blood should go in search of the air. 



Such was the object of my researches. Before giving an account 

 of them I think I ought to state the opinions of the different 

 anatomists respecting the dorsal vessel. 



Malpighi * has described the dorsal vessel in his excellent 

 anatomy of the silk-worm. He considered it as a long canal, 

 which in its length swells out or contracts, forming several small 

 oval tubes, which may be regarded as so many small hearts. But 

 here Malpighi was deceived by the successive contractions of the 

 dorsal vessel. What proves this are the remarks which he makes 

 himself. The movements, says he, of those parts of the dorsal 

 vessel, which we may consider as so many hearts, are very irregular, 

 and the liquid contained in it has often a retrograde motion. This 

 irregular motion cannot agree, as Cuvier has remarked, with a 

 principal organ of circulation. This single proof seems sufficient 

 to prevent us from considering the dorsal vessel as a heart. Malpighi 

 adds that he never perceived the least ramification in the dorsal 

 vessel; and in fact the figures which he gives of it (torn. ii. 

 tab. iii. fig. 4,) do not exhibit any. But how can we conceive a 

 circulation without vessels, and how can vvc give the name of heart 

 to a vessel which performs none of the functions of that kind of 

 ilation ? 

 Malpighi inquires next whether arteries proceed from this heart, 

 and whether they convey the blood to the whole body. As to tiie 

 bnmches which come from the dilatations of the dor-al vessel, and 

 which he calls auricles, be recognized them for trachea-. That they 

 are so is evident, as their extremities that touch the dorsal V€ I 



•» See hi. Opera Poidiuraa de Bonbyciboi, t. ii. p. i!0. 



