30 



BIOLOGY OF THE PROTOZOA 



than 1000 operations on Paramecium cavdatum have been success- 

 ful, but the percentage is greatly increased hy preliminary treatment 

 with neutral red. Other forms of ciliates on the other hand may 

 be cut in any plane, Uronychia transfiiga and Vroleptus mobilis 

 for example, reacting to such operations with all the physical prop- 

 erties of a piece of cheese. 



The more fluid Protozoa, when the form is not maintained by 

 resistant cortical differentiations react to physical properties of the 

 surrounding medium. When forces on all sides are equal, as in 



Fig. 8. — Euglypha alveolata {A), and Cochliopodium sp. (fi). (After Calkins.) 



suspended water-dwelling types like Actinophyrs sol, ActlnosphoB- 

 rium, many Radiolaria, etc., the form is spherical, or spherical also 

 in parasitic forms enclosed in the protoplasm of the host cell as is 

 the case with the majority of Coccidia. In all types, under certain 

 environmental conditions, or when continuously irritated, there is 

 a tendency to become globular and this is the form assumed by the 

 great majority' of Protozoa when they encyst. The spherical, or 

 homaxonic type, furthermore, is characteristic of the most gener- 

 alized representatives of all classes of Protozoa. 



