176 



THE PROTOZOA 



out from the cortical plasm and are then carried about in the 

 stream. 



In addition to the trichocysts, some of the Ciliata carry still more 

 effective weapons in the form of nematocysts. In Vorticella umbel- 

 laria (Clap. & Lach.), Engelmann described from twelve to twenty 

 pairs of capsules, each of which contained a coiled thread which, as 

 in the Ccelenterata, could be thrown out upon irritation. 



The cortical plasm may be considered the inner portion of the 

 ectoplasm, the outer portion of which forms the covering of the 

 animal, the membrane, cuticle, or pellicle. The latter is extremely 

 variable in thickness and in complexity. It is apparently homolo- 

 gous with the ex- 

 ternal membrane 

 of ordinary animal 

 cells, and, accord- 

 ing to Btitschli, is 

 formed by conden- 

 sation of the pro- 

 toplasmic ground 

 substance, and, as 

 Stein ('59) first 

 maintained, is in 

 no sense a secre- 

 tion. 1 Biitschli 

 ('88), Schuberg 

 ('87), and many 

 others regarded it 

 as the agglutina- 

 tion of the outer 

 thickened lamellae 

 of the external 

 alveoli into a continuous membrane. In forms where the cortical 

 plasm is absent, as in Hypotrichida, the cuticle, or, as Biitschli 

 prefers to call it, the pellicle, forms a thin coating to the cell 

 and lies directly upon the endoplasm. In many cases the outer 

 protoplasm either becomes changed into, or else secretes, an external 

 casing or house, which may be either loose or tight-fitting. This 

 covering may be of jelly (e.g. Ophrydium), or of chitin (e.g. Folli- 

 culina), or of a horny product without any mineral elements (e.g. 

 Coleps). In Coleps hirtus (Ehr.) the horn-like covering is tight-fitting, 

 and composed of separate pieces, which form four girdles about the 

 body (Fig. 93). Each girdle is composed of separate pieces, each of 

 which is straight on one edge and serrated upon the other in such a 



1 Cf. Stein ('59), p. 56. 



c 



Fig- 93- — Coleps hirtus Ehr. [MAUPAS ] 

 A. Side. B. One of the 15 rows of plates composing the test 

 C. Division-phase. 



