64 PROTOZOOLOGY 



trichites which have been torn away during the process of prey in- 

 gestion." Whether the numerous 12-20/i long needle-like endoskele- 

 tal structures which Kahl observed in Remanella (p. 584) 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 regularly 

 at right angles to the body surface, while in forms, such as Cyclo- 

 gramma they are situated obliquely (Fig. 278, c). In Frontonia 

 leucas (Fig. 22), Tonniges found that the trichocysts originate 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 col- 

 loidal 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 fila- 

 mentous 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 under the influence of certain stimuli 

 the expansion of the colloidal substances results in the extrusion 

 of the trichocysts through the pellicle. The fully extruded tricho- 

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

 leucas are about 6m long, but when extruded, measure 50-60m in 

 length, and those of Paramecium caudatum may reach 40m in 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 tricho- 

 cysts contained a toxic fluid and named them toxicytes. Recently 

 Hayes found that the exploded trichocysts (Fig. 22) could be dis- 

 tinctly seen and suggested that these trichocysts themselves may be 

 toxic. 



