406 



Note on a Gregarine (.{(/(/regata inachi n. sp.) which 



may cause the parasitic castration of its host 



(Inachus (Jorsettensis), 



By 

 (ieoffrey Smith, 



New College, Oxford. 



With piate 26. 



1. The effect of the parasite ou its host. 



The fact that tbe presence of a parasite may profoundly modify 

 the sexual development of its host was first made known by Giard, 

 and in a series of papers (see especially 1 and 2) this author has 

 from time to time uotified the wide spread oecurence of what he 

 calls "castration parasitaire". It apjiears fiom his observations that 

 a number of different parasites belonging to widely ditferent classes 

 of animals can bave this etfect on their various hosts, so that it is 

 evident that we are dealing with a general process of deej) mea- 

 ning. The castration brought about by these various parasites is 

 found to atfect the primary and the secondary sexual characters of 

 the hosts, causing the gonad to be reduced or even totally to dis- 

 appear in infected individiials, while externally the infected males 

 assume characters })roper to the female. and tbe infected females 

 show a degenerate condition of their secondary sexual characters. 

 No clear case has as yet been adduced of the female assuming 

 distinctively male characters under the iufluence of parasitic 

 castration. 



The degeneration of the gonad may be brought about directly 

 by the i)arasite attacking this organ, but in the great majority of 

 cases the parasite is situated in a different part of the body to the 

 gonad, and. affects this organ indirectly in some unknown manner. 



