MORPHOLOGY 63 



Whether the numerous 12-20^ long needle-Hke endoskeletal 

 structures which Kahl observed in Remanella (p. 522) are modi- 

 fied trichites or not, is not known. 



In numerous ciliates, there is another ectoplasmic organella, 

 the trichocyst, which is much shorter, though somewhat similar 

 in general form. As seen in a Paramecium, the refractile fusiform 

 trichocysts are embedded in the ectoplasm and arranged at right 

 angles to the body surface, while in forms, such as Cyclogramma 

 they are situated obliquely (Fig. 240, c). In Frontonia leucas 

 (Fig. 22), Tonniges found that the trichocysts originated in the 

 chromatinic endosomes of the macronucleus and development 

 takes place during their migration to the ectoplasm; on the other 

 hand, Brodsky believes that the trichocysts are composed of 

 colloidal excretory substances and are first formed in the vicinity 

 of the macronucleus, becoming fully formed during the course of 

 their migration toward the periphery of the body. In species of 

 Prorodon, Kriiger recently observed that the rod-like trichocysts 

 of these ciliates are composed of a cylindrical sac containing a 

 long filament which is arranged in a manner somewhat similar to 

 the polar capsule of cnidosporidian spores. The end facing the 

 body surface is filamentous and connected with the pellicle. 



The extrusion of the trichocysts is easily induced by means of 

 mechanical pressure or chemical (acid or alkaline) stimulation, 

 though the mechanism of extrusion is not well understood in all 

 forms. Brodsky maintains that the fundamental force is not the 

 mechanical pressure, but that the expansion of the colloidal sub- 

 stances results under the influence of certain stimuli in the ex- 

 trusion of the trichocysts through the pellicle. The fully extruded 

 trichocysts are needle-like in general form. The trichocysts of 

 Frontonia leucas are about G/j, long, but when extruded, measure 

 50-60/x in length, and those of Paramecium caudatum may reach 

 40m ill length. 



Dileptus anser feeds on various ciliates through the cytostome, 

 located at the base of the proboscis, which possesses a band of long 

 trichocysts on its ventral side. When food organisms come in 

 contact with the ventral side of the proboscis, they give a violent 

 jerk, and remain motionless. Visscher saw no formed elements 

 discharged from the trichocysts, and, therefore, considered that 

 these trichocysts contained a toxic fluid and named them toxi- 

 cytes. Recently Hayes found that the exploded trichocysts (Fig. 



