CIRCULATION IN THE CRUSTACEA. 257 



superior classes of animals, performs so impor- 

 tant an office in the circulation of the blood, 

 namely, the heart: and this name, indeed, is 

 given by Cuvier, Morren, and others, to these 

 dilated portions of the vascular systems of the 

 higher orders of Annelida.* 



Here, also, the statements of different anato- 

 mists are at variance, with regard to the direc- 

 tion taken by the blood while circulating in the 

 vessels : Home and Duges represent it as pro- 

 ceeding forwards in the dorsal, and backwards 

 in the abdominal vessels ; a course which im- 

 plies its descent along the lateral communicating 

 vessels just described ; while De Blainville and 

 Morren ascribe to it a course precisely the 

 reverse. Amidst these conflicting testimonies, 

 it is extremely difficult to determine on which 

 side the truth lies ; and a suspicion will natu- 

 rally arise, that the course of the blood in the 

 vessels may not be at all times uniform, but may 

 be liable to partial oscillations, or be even com- 

 pletely reversed, by the operation of particular 

 disturbing causes. 



The larger Crustacea possess a circulatory 

 apparatus still more extensive and complete, 

 accompanied by a corresponding increase in the 

 energy of the vital functions. As we follow this 



* It is remarkable that the blood in most of the Annelida has 

 a bright scarlet colour, and resembles in this respect the blood 

 of vertebrated animals, 



VOL. n. s 



