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 



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 



