148 



PROTOZOOLOGY 



zation and multiplication as in Colpoda cucullus (Kidder and Claff, 

 1938). Because of the latter condition and also of the failure in at- 

 tempting to cause certain Protozoa to encyst under experimental 

 conditions, some suppose that certain internal factors play as great 



Encystment of Lopho)nonas blattarum, X1150 (Kudo). 



a part as do the external conditions in the phenomenon of encyst- 

 ment. Ordinarily a single cyst wall seems to be sufficient to protect 

 the protoplasm against unfavorable external conditions. In some 

 cases there may be a double cyst wall, the inner one usually being 

 more delicate. The cyst wall is generally composed of homogeneous 

 substances, but it may contain calcareous scales as in Euglypha 

 (Fig. 70). While chitin is the common material of which the cyst wall 



Fig. 70. Encystment of Euglypha acanthophora, X320 (Kiihn). 



is composed, cellulose makes up the cyst membrane of numerous 

 Phytomastigina. 



The capacity of Protozoa to produce cyst is probably one of the 

 reasons why they are so widely distributed over the surface of the 

 globe. The minute protozoan cysts are easily carried from place to 



