10^. Parasites of the Parasites. 



dition for hermaphrodites in general. Why then are fixed animals so commonly hermaphro- 

 dites? It has been suggested that by each animai being first a male and then a female a 

 greater percentage of eggs can be fertilized, but this supposed advantage on examination is 

 seen to be illusory in those bermaphrodites which ripen tbeir male and female generative 

 products at different times, and these are by far the majority. In fact unless mutuai fertili- 

 zation of hermaphrodites in pairs can occur, as it may occur in the earthworm, the chances 

 of fertilization are not any greater in an hermaphrodite than in a dioecious species. Pro- 

 tandric hermaphroditism therefore from this point of view is merely a violation of the prin- 

 ciple of economy of labour and has no particular advantage that we can see. It has been 

 already stated that in Danalia curvata a special apparatus of phagocytic cells is present for 

 the sole purpose of absorbing the remains of the testes of the Cryptoniscus larva, and in a 

 large majority of cases it was found that the testes after fixation on the host contained a 

 large quantity of sperm which could not be of any use for the propagation of the species, 

 and this fact certainly points to a disharmony in the sexual organization of the animai. So 

 far then we have been unsuccessful in finding an adaptive meaning in the hermaphroditism 

 of fixed animals, and it is difficult to suggest any other alternative. It appears on the con- 

 trary that the hermaphrodite state is one from the naturai implication of which, i. e. the 

 implication of self-fertilization, ali hermaphrodites take special precautions to escape. It may 

 be mentioned parenthetically that Maupas in his study of the Reproduction of Nematodes (4) 

 was equally unable to find an adaptive meaning in the secondarily developed hermaphroditism 

 of certain species, because in these forms he was able to prove that actually fewer eggs were 

 fertilized than would. have been the case if the normal cross-fertilization of ordinary females 

 by males had been retained. 



In Chapter 5 of this Monograph I am able to prove that a perfectly developed herma- 

 phrodite condition may be called forth in a normally dioecious animai through the influence 

 of the conditions of life, in this case through a fundamental alteration of the metabolic con- 

 ditions effected by the presence of a parasite. 



In view of this fact, and taking into consideration the extreme difficulty experienced 

 in attempting to account for hermaphroditism as a special reproductive adaptation, we may 

 adopt the view that the hermaphroditism of fixed animals has followed as a necessary 

 result of the conditions of their life, and not as a special adaptation for securing the 

 increased propagation of the species. How the state of fixation has effected this change in 

 the reproductive system we can only vaguely guess, but it may be pointed out that fixation 

 necessarily implies a very uniform and passive condition of life, and that it also implies a 

 degenerative return to a simpler and less highly differentiated organization in general, and in 

 this process the reproductive system seems to have been involved. According to this view 

 the hermaphroditism of fixed animals is regarded as a degenerative state called into being as 

 the result of an immobile inactive existence in which ali complicated differentiation does as 

 a matter of fact tend to be lost. Whatever may be the cause of the ordinary differentiation 



