DEGRADATION AN 7 D PARASITISM 27$ 



negative organism, for it possesses no separate micro- 

 nuclei, no cytostome, cytopharynx, or cytopyge, and 

 does not reproduce like the majority of Ciliates. 

 During summer and autumn one species parasitic in 

 the rectum of the frog reproduces by a special method 

 of division. There is a great increase in the number of 

 nuclei, and the body divides also, so that two daughter 

 forms are produced, each of which, after growing full- 

 sized again, repeats the process. In spring the Opalina 

 divide rapidly, but do not increase much in size 

 before dividing again, so that they constantly become 

 smaller. Finally, tiny forms, containing three to six 

 nuclei, encyst and pass from the frog with the 

 faeces. Further development occurs if the cysts are 

 swallowed by tadpoles, when the organisms emerge 

 from the cysts, divide into uninucleate individuals, 

 which, later, unite together in pairs. The zygotes 

 thus produced encyst, and within the cyst, nuclear 

 fusion occurs, and finally the ciliates leave the cysts 

 and grow into the adult forms. 



The parasitism of the Ciliata has led to degenera- 

 tion of the structures concerned with nutrition in 

 many cases, and the limit of degeneration is found in 

 Opalina. Correlated with the simplification of the 

 vegetative structures, there is the great power of 

 multiplication asexually within the host, and the 

 production of cysts, either with or without sexual pro- 

 cesses, to bring about the transference to new hosts. 

 The Ciliata form an interesting group, the parasitic 

 members of which may be shown, on further research, 

 to be more numerous than is at present suspected. 

 They are well worthy of extended investigations. 

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