MORPHOLOGY 71 



attachment of the undulating membrane, a rod-like structure which 

 has been known as costa (Kunstler) and which, according to Kirby's 

 extensive study, appears to be most highly developed in Pseudo- 

 trypanosoma and Trichomonas. The staining reaction indicates that 

 its chemical composition is different from that of flagella, blepharo- 

 plast, parabasal body, or chromatin. 



In the gymnostomatous ciliates, the cytopharynx is often sur- 

 rounded by rod-like bodies, and the entire apparatus is often called 

 oral or pharyngeal basket, which is considered as supportive in 

 function. These rods are arranged to form the wall of the cyto- 

 pharynx in a characteristic way. For example, the oral basket of 

 Chilodonella cucullulus (Fig. 312, c, d) is made up of 12 long rods 

 which are so completely fused in part that it appears to be a smooth 

 tube; in other forms, the rods are evidently similar to the tubular 

 trichocysts or trichites mentioned below. 



In numerous holotrichs, there occur unique organelles, trichocysts, 

 imbedded in the ectoplasm, and usually arranged at right angles to 

 the body surface, though in forms such as Cyclogramma, they are 

 arranged obliquely. Under certain stimulations, the trichocysts "ex- 

 plode" and form long filaments which extend out into the surround- 

 ing medium. The shape of the trichocyst varies somewhat among 

 different ciliates,, being pyriform, fusiform or cylindrical (Penard, 

 1922; Kriiger, 1936). They appear as homogeneous refractile bodies. 

 The extrusion of the trichocyst is easily brought about by means of 

 mechanical pressure or of chemical (acid or alkaline) stimulation. 



In forms such as Paramecium, Frontonia, etc., the trichocyst is 

 elongate pyriform or fusiform. It is supposed that within an expansi- 

 ble membrane, there is a layer of swelling body which is responsible 

 for the remarkable longitudinal extension of the membrane (Kriiger) 

 (Fig. 21, a). In other forms such as Prorodon, Didinium, etc., the 

 tubular trichocyst or trichites are cylindrical in shape and the mem- 

 brane is a thick capsule with a coiled thread, and when stimulated, 

 the extrusion of the thread takes place. The trichites of Prorodon 

 teres measure about 10—1 1 yu. long (Fig. 21, d) and when extruded, 

 the whole measures about 20 /x; those of Didinium nasutum are 15- 

 20m long and after extrusion, measure about 40 m in length (Fig. 21, 

 e,f). In Spathidium spathida (Fig. 21, c), trichites are imbedded like 

 a paling in the thickened rim of the anterior end. They are also 

 distributed throughout the endoplasm and, according to Woodruff 

 and Spencer, "some of these are apparently newly formed and being- 

 transported to the oral region, while others may well be trichites 

 which have been torn away during the process of prey ingestion, " 



