32 



BIOLOGY OF THE PROTOZOA 



make-up. Membranes of living substance, as in Cochliopodiym 

 (Fig. 8) and the majority of flagellates and ciliates; of lifeless chitin 

 as in Allogromia oviform e (Fig. 9) or the lifeless materials secreted 

 by the cell and deposited on it, are responsible for the forms assumed 

 by many Protozoa. Even delicate types such as Clathrulina elegans 

 and the majority of Heliozoa retain their forms by virtue of the pro- 

 tecting shells of lifeless materials deposited on a chitinous membrane. 

 The protoplasmic bodies of many of the fresh water shelled rhizo- 

 pods are relatively dense like that of the naked Amoeba verrucosa and 





B 





X 



'■^^Jv'""//! 



Fig. 10.- 



-Pscudodifflugia sp. circular mouth opening and mosaic shell {A). B, division 

 stage. (Original.) 



are more or less globular or pyriform in shape. On such a proto- 

 plasmic basis the shells of Difflugia species, Euglypha, Cyphoderia, 

 Centropyxis, Arcella, etc., are deposited and these, once formed, are 

 never changed (Fig. 10). Only rarely are these shelled rhizopods 

 flattened or discoid as in Ilyalodiscus. 



The typical form in many shell-bearing or skeleton forming rhizo- 

 pods may be due in its last analysis to the finer structure of the pro- 

 toplasmic body in which the skeleton or shell parts are deposited. 

 Dreyer (1892) has given much evidence to show that the form and 

 size of the elements making up the skeletal or shell parts depend. 



