26 General Morphology of the Protozoa 



also in the stalks of certain ciliates. The stalk-muscle of Zoothamnium 

 extends spirally within a sheath continuous with the protoplasm of the 

 body. Between the sheath and the surface of the stalk, there is a matrix 

 filled with elastic fibrils which arise from a differentiated area, the 

 scopula, in the aboral body wall (182). The stalk-muscle extends almost 

 to the base of the stalk, where it is attached by a fibrillar bundle to the 

 basal disc. The individual stalk-muscles of the Carchesium colony are 

 attached to the bases of their own stalks, so that each stalk-muscle 

 contracts independently. 



TRICHOCYSTS AND NEMATOCYSTS 



Trichocysts are cortical structures reported in certain ciliates and 

 flagellates. Trichocyst-bearing Holotrichida are represented by several 

 dozen genera. In addition, trichocysts have been reported in some Het- 

 erotrichina (e.g., Blepharisma) and in Strombidiiun among the Oli- 





# ^ 





Fig. 1. 14. A. Nematocyst of Polykrikos; xl450 (after Kofoid and Swezy). 

 B. Fusiform and spherical trichocysts of Gonyostomum semen; diagram- 

 matic (after Chadefaud). C, D. Trichocysts of Dileptus anser before and 

 after discharge; x3080 (after Hayes). E. Developing and mature trichocysts 

 in Parayneciiim caudatum; diagrammatic; xl280 (after Jacobson). Key: c, 

 cortex; ch, chromatophore; /, fibril (A), fusiform trichocyst (B); 5, spherical 

 trichocyst; st, stylet; t, trichocyst; td, developing trichocyst. 



gotrichina (200). Trichocysts may be widely scattered over the body 

 (Parameciiwi), limited to the peristomial area (Dileptus), or borne on 

 tentacles or papillae [Actinobolina, Legendrea). Development of tricho- 

 cysts from macronuclear granules has been reported. However, this 

 phenomenon has not been confirmed (100), although developing tricho- 

 cysts (Fig. 1. 14, E) appear in the cytoplasm of Frontonia leucas and 

 Paramecium caudatum. The outgrowth of trichocysts from "trichocysto- 

 somes," granules produced by division of basal granules, also has been 

 reported (150). So-called protrichocysts of various ciliates have been in- 

 terpreted also as deposits of tectin, used in formation of the cyst mem- 

 brane or the lorica (12, 200). 



