CA TA GENESIS. 213 



At last it was discovered that the small Cyclops-like 

 males lead an independent life and swim about freely 

 by means of their four pairs of swimming feet, and 

 that the females in their copulatory stage resemble the 

 males, and that it is only after copulation that they 

 (the females) become parasitic and undergo the con- 

 siderable increase in size and modification of form 

 which characterizes the female with egg-tubes." 



A degeneracy of the females of a remarkable char- 

 acter occurs in the insects of the order Strepsiptera. 

 Here the female during the larval stage, bores its way 

 into the body of a hymenopterous insect and soon un- 

 dergoes a moult. At this time they shed their three 

 pairs of well-developed legs, and become a parasitic 

 maggot, which lives on the body of the host. The 

 males do not undergo this degeneracy but retain the 

 six legs and two pairs of wings common to the class 

 Insecta. 



A notorious example of degeneracy among the Mol- 

 lusca is offered by the Entoconcha inirabilis. Says J. 

 S. Kingsley : " So greatly has parasitism altered the 

 form of the body, and all of the organs, that the proper 

 position of this form among the gastropods is far from 

 certain, some placing it near Natica. Indeed, were it 

 not for the characters afforded by the young, its posi- 

 tion among the MoUusca would not be suspected. 

 Some thirty years ago [before 1885] Johannes Miiller 

 found in some specimens of Synapta digitata an inter- 

 nal worm-like parasite, attached by one extremity to 

 the alimentary canal, while the other end hung free 

 in the perivisceral cavity." " In one specimen of Syn- 

 apta out of one or two hundred this strange form oc- 

 curs. It is a sac, the upper part bearing the female, 

 and the lower the male reproductive organs, while the 



