THE CRAYFISH AND ITS ALLIES 



121 



wise true, to an equal degree, of the internal organs. The 

 internal organs of Nereis are repeated in each segment; but 

 in the crayfish the egg-ducts lie in one segment, the heart 

 in another part of the body, and so on. Some of the seg- 

 ments have given up one or more functions to perfect a 



FIG. 117. Eyestalks of a Decapod dissected out. On the right an antenna 

 has regenerated in place of the amputated eye. opt., optic nerve. After 

 Herbst. 



single one in which it has specialized. There has been a 

 division of labor between the different parts of the body, 

 and in consequence a greater perfection in the performance 

 of each function. More perfect fulfilment of function is 

 the result of physiological division of labor, just as a higher 

 civilization is the result of individual division of labor. 



