40 MEMOIRS OF 



beloved object, or shed tears at the sight of virtue in distress. 

 These effects of the nervous system arise from the numer- 

 ous communications of particular nerves, called sympathet- 

 ic, existing between divers ramifications of the general 

 trunk; and by means of which impressions are more rapidl}^ 

 transmitted than by means of the brain. These knots of 

 nerves, which, when enlarged, bear the name of ganglions. 

 are a species of secondar}^ brains, and are always of greater 

 size, and in a greater number, as the proportion of the prin- 

 cipal brain is less considerable." 



When, in the third division, M. Cuvier treats of the differen- 

 ces of the organs of animals, he observes, that the circulation 

 of the blood furnishes the most important variations. " First, 

 there arc animals Vv^hich have no blood, such as insects and 

 zoophytes ; and, secondly, those which have it possess it in 

 a double or simple mode. That is called double circulation 

 when no part of the venous blood can re-enter the arterial 

 trunk until it has made a certain circuit in the organ of 

 respiration, which must be formed by the expansion of two 

 vessels, the one arterial and the other venous, nearly of 

 equal size, but shorter than the two principal vessels of the 

 body. Such is the circulation of man, mammalia, birds, 

 fishes, and many mollusca. In simple circulation, a great 

 part of the venous blood re-enters the arteries without 

 passing through the lungs, because this organ receives but 

 one expansion from one branch of the arterial trunk. 

 Such is the circulation of reptiles. There are yet other 

 differences in the existence and position of hearts, or muscu- 

 lar organs destined to impel the blood. In simple circula- 

 tion there is never more than one : but when the circulation 

 is double, one part is sometimes seated at the base of the 

 principal artery, and the other at that of the pulmonary 

 artery ; and sometimes there is only one of these two parts. 

 In the first case, the two hearts, or, rather the two ventri- 

 cles, may be united in one single mass, as in man, mamma- 

 lia, and birds ; or they may be separated, as in the cuttle- 

 fish. AYhen there is only one ventricle, it is either placed 

 at the base of the artery of the body, as in snails and other 

 mollusca, or at the base of the pulmonary artery, as in 

 fishes. 



" Tiie organs of respiration are equally fertile in remark- 

 able differences. When the element wdiich is to act on the 



