3q8 Louise Hoyt Gregory 



June 13 9 cysts were put in rain water at room temperature. 

 14 5 came out of cysts. 



From these experiments it will be seen that there is no definite 

 rule in regard to the numbers that can be forced from the cyst. 

 There is a great deal of individual diflPerence, and the same proc- 

 esses that will be effective in one case will have no results in 

 another case, even though the age and the environment have been 

 the same. Generally, however, starved forms will always encyst, 

 and a change in environment, either of food or of temperature, 

 will cause the encysted form to assume its free living existence. 

 Minchin has suggested the cause of this may be the influence of 

 salts in the solution upon the membrane, an external cause, or the 

 stimulus may come from the interior of the cyst acting on the 

 membrane, the original stimulation coming from the new environ- 

 ment. It either case the cause would be primarily an external 

 one. 



In general, the reproductive and protective cysts differ but little 

 from one another save in the thickness of membrane and presence 

 of food vacuoles. Rhumbler has found a more important differ- 

 ence in the presence of a definite opening in the reproductive cysts 

 of Colpoda cucuUus. Since Rhumbler's observation is the only 

 evidence, we may consider this an exception. In Colpidium also 

 a reproductive cyst may become a permanent protective cyst, and 

 in Tillina I have seen individuals that had encysted for division 

 secrete a thicker membrane, until finally a permanent cyst was 

 formed. This may happen either before or after division; in the 

 latter case each individual secretes a thick membrane. 



There is also a close relation between the reproduction within 

 the simple division cysts and the sporulation cysts. If the divi- 

 sions are simultaneous, the process might be regarded as sporula- 

 tion, if, however,they are successive, the process is division. The 

 conditions in Tillina must be considered an intermediate stage, for 

 in reproduction, resulting in the formation of four individuals, the 

 divisions are not simultaneous, but nevertheless, they follow each 

 other so rapidly, that the second plane appears before the first 

 division has been completed, and the four individuals mature at 



