DIVISION AND :\rORPIIOGENESIS 



37 



tomite. This tomite will escape the cyst, and after a short 

 free life forms a new cyst on a Nebalia. This large phoront 

 has lost the power to divide without an external stimulus. 

 Division will start only some hours before the ecdysis of 

 the host. It is apparently induced by some substance which 



Phoront 



Apotomite 



Grown-up 5 

 trophont 



X 



Apotomont 



Fig. 11. Apotomy. The food intake by the trophont has been small. 

 The cycle is completed without any division. Apotomy may occur 



in many species. 



is excreted by the host at this period. Nevertheless, this 

 induced division proceeds normally as in other species. 

 However, after the last division, it is not the tomital struc- 

 ture which is produced, but the structure of the trophic 

 phase. 



When division takes place normally, the ciliate is or- 

 ganized into the tomital structure. When division takes 

 place after a resting period and is induced by the ecdysis of 

 the host, the ciliates have the structure of the trophont. 



The situation is somewhat the same in Synophrya hyper- 

 trophica. The life cycle is represented on the diagram. 



