GENERAL SKETCH 



39 



sensory and tactile organs (cirri}, or protective structures like hooks, 

 spines, and tentacles (Fig. 12, BG\ see also Fig. 16). 



Like many of the cells which constitute the tissues of higher ani- 



A 



C 



Fig. 12. Ectoplasmic modifications. 



A. Amceba tentaculata. [GRUBER.] B. Clepsidrina munieri. [SCHEWIAKOFF.] C. Tri- 

 chocysts. [SCHEWIAKOFF.] D. Nematocysts from the sporozoon Myxobolus. [BALBIANI.] 

 E, F, G, attaching hooks and spines from different Gregarinida. [WASIELEWSKY.] 



mals, the protozoan body has the power of forming by chemical pro- 

 cesses over and above those which relate merely to nutrition, various 

 products which are secreted just within the peripheral plasm, where 

 they usually form a protective armor in the shape of shells, tests, or 

 " houses." The materials thus formed within the cell-body may be 

 chitin (composed of C, H, N, and O, and supposed to be a deriva- 

 tive from carbohydrates, but the exact formula is in dispute), cellulose 



