208 



THE THEORY OF EVOLUTION 



the females, and only the females, attach themselves 

 after the pairing, do the retrogressive steps begin which 

 lead to the assumption of the almost limbless state. 

 The males remain much more crab-like, they die after 

 the pairing, their function being fulfilled ; the females, 

 on the other hand, must now provide the eggs with 

 nutrition, and therefore survive. Since they can do 



FIG. 42. Young 

 Flounder be- 

 fore the shift- 

 ing of the eye. 

 (mag.40diam.) 



FIG. 43. Flounder 

 when eye is quite 

 shifted. 



FIG. 44. Commence- 

 ment of the shifting 

 in the Turbot. (mag. 

 10 diam.) 



that as parasites without organs of locomotion or 

 sense, these abort as superfluous. They were therefore 

 at first Rudder Crabs (Ruderkrebse) in their appear- 

 ance, as the males still are, and their amorphous form 

 is no original one, but one acquired by parasitism. 



Many similar examples might be quoted as, for 

 instance, the transfer of the right eye to the left side 

 in the young of flatfish which, as adults, lie on the right 

 side and have both eyes on the left side (Figs. 42, 43, 44, 

 45). If that were originally so, why have the flatfish an 



