CRUSTACEA. 



plished in the lobster, in a different, and, perhaps, more efficient 

 manner. Fig. 157. 



(370.) In the 

 lowest Crustacea the 

 heart is a long dor- 

 sal vessel, not very 

 dissimilar in form 

 and disposition from 

 that of insects; but 

 of course giving off 

 arteries for the distri- 

 bution of the blood, 

 and receiving veins 

 through which the 

 blood, having ac- 

 complished its cir- 

 cuit, is returned. 



In tie Decapoda 

 the organ becomes 

 more centralized, and 

 in the lobster (Jig. 

 157, e) the heart is 

 found to be an oval 

 viscus, situated in 

 the mesial line of 

 the body, beneath 

 the posterior part 

 of the cephalo-tho- 

 rax; it is composed 

 of strong muscular 

 bands, and contains 

 a single cavity of 

 considerable size. 

 The contractions of 

 this heart are very 

 vigorous, and may 

 readily be witnessed 

 by raising the super- 

 jacent shell in the 

 living animal. 



Several large arte- 



