THE INFUSORIA 385 



tion of Dendrosoma therefore appears to be a process of multiple, 

 internal, unequal fission. In several species of Ephelota and 

 others, not one but several small daughter seg- 

 ments are formed simultaneously (Figs. 34 and 

 21) at the free extremity of the body, and 

 these are liberated when they have reached a 

 certain size. 



In the literature of ACINETARIA the smaller 

 daughter segments receive the names "buds," 

 "gemmulae," or "embryos," and the processes by 

 which they are formed are called internal or 

 external, multiple or simple, gemmation. Whilst 

 recognising the utility of retaining such a name as * 

 gemmulae for them, it must not be forgotten that the for liberation. (From an 

 process of gemmation in the Heterokaryota is essen- paS^'bf^^As'h- 

 tially the same as that of fission. worth.) 



ENCYSTMENT AND SPORE-FORMATION. There can be no doubt 

 that a very large number of the Infusoria have the power of 

 encystment. The encystment may be accompanied by reproduction, 

 a large number of small individuals being formed during the period 

 and escaping from the cyst wall at the end of it, or it may be 

 simply a resting-stage from which only one individual escapes. In 

 many CILIATA (Colpoda, Prorodon, etc.) both kinds of cysts may 

 occur in the same species, and it is difficult to draw any definite 

 line between them, but in the majority of species it seems probable 

 that the cysts are either purely resting cysts or reproductive cysts. 



Encystment may be caused by the concentration of the salts in 

 water previous to drought, as proved experimentally by Cienkowsky ; 

 by the diminution in the food supply, as proved by Maupas for the 

 OXYTRICHINAE ; or, in the entozoic forms, by the change from their 

 natural habitat into fresh-water. Encystment is never, in any 

 Ciliata, a necessary sequence of conjugation. In the process of 

 encystment the cilia are withdrawn and the protoplasm of the body 

 contracted into a spherical or elliptical shape, while one or more 

 walls are secreted by the pellicle. The outer wall or ectocyst may 

 be soft and gelatinous as in certain Yorticellina, or it may be hard, 

 facetted, or thorned (Fig. 73). The inner walls or endocysts are 

 usually thin and membranous. 



The resting cysts are capable of resisting the effects of dry air 

 for a considerable length of time. Nussbaum, for instance, found 

 that the cysts of Gastrostyla rorax were alive at the end of two 

 years, and Maupas successfully hatched out Gastrostyla steinii from 

 cysts that had remained dry in a watch-glass for twenty -two 

 months. Nussbaum, however, found that in twelve years all the 

 encysted Gastrostyla vorax were dead. 



25 



