68 INTERNAL SECRETIONS 



infected earthworm cannot replace the testicle or control the 

 male sexual characters. The influence which the ovary and 

 the testicle in the earthworm exert on its somatic characters 

 are different from one another; the action of the gonads on the 

 body is evidently a sex specific one. We shall discuss the 

 question of sex speciiity more fully later on. 



The observations of Sollas have been extended experimentally 

 by Harms (1914). Experimental castration can be performed 

 in Lumbricidae without great difficulty, the male and female 

 gonads being localised in different segments; male or female 

 castration can be performed by cutting away male or female 

 segments and sewing together the remaining segments. Harms 

 showed that the clitellum disappears after male castration, but 

 remains intact after female castration. Some of the animals 

 operated on by Harms lived for nine months after the operation. 



In opposition to the observations related above is a statement 

 recently made by Dvagoiu and Faure-Fremiet (1920) about a 

 female of Ascaris megalocephala} They found an individual in 

 which no generative cells were present in the ovary, the wall 

 only being visible. Nevertheless, the oviducts and the uterus 

 were normal. 



Observations on Planaria have been made by Vandel (1920). 

 In certain species of Planaria the gonads are situated princi- 

 pally in the front or in the prepharyngeal part of the body, 

 whereas the copulatory organs are to be found in the posterior 

 or postpharyngeal region. Vandel cut off an anterior frag- 

 ment of the body in order to make observations on regenera- 

 tion phenomena. He found that an anterior fragment could 

 undergo regeneration and develop very rapidly in about 15 

 to 25 days a new posterior part with copulatory organs. Now, 

 in one case regeneration took place, but no trace of copulatory 

 organs could be found in the newly-formed posterior part 

 even five weeks after the operation. This was confirmed by 

 histological examination, which revealed only the presence 

 of intestinal branches. But the most interesting result of the 

 histological examination was that the germinative cells in the 

 gonads of the anterior part were degenerated and destroyed, 

 evidently by parasites, as Vandel thinks. He concludes from 

 this observation that the castration did not prevent the 

 process of regeneration or the formation of a new posterior 



^A Nematode or thread-worm parasitic in the horse. 



