CHAPTER ^ 



The Complicated Life Cycle 

 of Gymnodhiioides inkystans 



We are now in a position to consider some apostomatous 

 ciliates.* This is a very homogeneous group, primarily 

 associated with Crustacea. Many of these ciUates have two 

 hosts. All have very remarkable and unique properties. 

 They show a complicated life cycle, each phase of which is 

 characterized by a peculiar structure that is the conse- 

 quence of important movements of the ciliary system. On 

 the gills of the hermit crab, Eupagurus hernhardus, are nu- 

 merous cysts of the ciliate Gymnodinioides inkystans. This 

 is the phoretic phase or phoront. Excystation occurs only 

 at the molt of the host, and the small ciliate penetrates the 

 discarded exoskeleton. This is the trophic stage or tro- 

 phont. In 6 to 10 hours the cihate has increased its volume 

 up to 32 times. The trophont then escapes from the exo- 

 skeleton and after some hours encysts and divides. Let us 

 call this stage tomont. The small ciliates or tomites thus 

 formed escape from the cyst and swim actively. They may 

 enjoy a free life for 6 to 8 days. If they find a crab, they 

 encyst on the teguments; if not, they die. 



The trophic phase corresponds to the ingestion and con- 

 centration by the ciliate of the violet astacin-protein of the 

 crab. During this phase, the cytoplasm of the trophont is 



*A11 the data on these cihates are taken from E. Chatton and A. 

 Lwoff's extensive monograph (1935). A good summary of this work 

 has been given l)y H. B. Kirby in Calkins and Summer's book, Protozoa 

 in Biological Research. 



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