1815.] On the Uses of the Dorsal Fessel 36S 



"Article X. 



Observations on the Uses of the Dorsal Vessel, or on the Infiuence 

 vjhick the Heart exercises in the Organization of articulated 

 jlnimals, and on the Changes which that Organization expe-* 

 oiences when the Heart or the Organ of Circulation ceases to 

 exist. By M. JNIarcel de Series. 



(Continued fr»m p. 199.) 



This last series of researches being finished, it remained to de- 

 termine the cause of the contractions and dilatations of the dorsal 

 vessel, and of what importance that vessel was to the general eco- 

 nomy of insects. These contractions and dilatations might depend 

 on various causes, or only upon the peculiar structure of that organ 3 

 though it was difficult to adopt such an opinion, because the ab^ 

 sencc of vascular vessels announced that the humour contained in 

 it lid not circulate. To determine the point 1 began by examining 

 what influence the muscles which surround the dorsal vessel might 

 have upon its contractions. 



The mole cricket, being a very lively insect, was chiefly em- 

 ployed by me in these researches. Tlie dorsal vessel being brought 

 in view, 1 removed the abdominal muscles (and the adipose mem- 

 branes of necessity) in the middle part of the abdomen, while 1 left 

 the dorsal muscles cjuite entire in the upper and lower part of the 

 abdomen. This being done, I remarked that the dorsal vessel 

 always contracted in those parts where the muscles had not beea 

 removed, and these contractions were the less lively the nearer they 

 came to the muscles that had been removed. However, by de- 

 grees, some contractions took place in the parts of the dorsal vessel 

 from which the muscles had been removed ; but they were always 

 weak, and seemed to proceed from portions in which the muscles 

 still existed. 



In other cases I removed entirely the dorsal muscles ; then the 

 contractions of the dorsal vessel became weaker by degrees, and 

 ceased at last, tliough after a very considerable interval. Dr. En- 

 contre* was so good, at my request, as to repeat these experiments. 

 He observed that, after removing the dorsal muscles, the contrac- 

 tions of the dorsal vessel diminished i)y degrees in the rings from 

 which tliese muscles had been removed ; wiiile they continued still 

 strong in those rings where the muscles still remained. In a ring 

 in which he had kit only some traces of muscle, liie dorsal vessel 

 still continued to contract, when its contractions had ceased in all 

 the parts fn»m whieli the muscles liad been removed. 1 must re- 

 mark, that the inseclh sut)iccted to tliese experiments are not dead, 

 when all tlie dorsal vessels have been removed; liut wiiat is still 



* He la thr. Boii o( M. Diiuicl Eiicuiilre, known widi eol«t usi a umtliematlciau. 

 Vol. V. N" V. 2 A 



