General Morphology of the Protozoa 27 



The trichocysts of Dileptus gigns (215) show no internal organization 

 and form no detectable structures upon discharge. These trichocysts 

 (toxicysts), which change shape during contortions of the ciliate and be- 

 come almost spherical under pressure of a coverslip, are believed to 

 contain a fluid. Comparable trichocysts are found in the tips of retrac- 

 tile tentacles in Actinobolina (225), and the flask-shaped trichocysts of 

 Conchophthirhis mytili (116) also may be similar to those of D. gigos. 



Trichocysts of certain other ciliates are discharged as recognizable 

 structures. Such is the case in Legendrea, Frontonia, Paramecium, Pror- 

 odon, and Dileptus anser. In electron micrographs (101, 102), discharged 

 trichocysts of Paramecium show a pointed tip resembling a golf tee, and 

 a transversely striated shaft. The trichocyst of Dileptus anser consists of 

 a thread-like extension into the cytoplasm and a bulbous portion which 

 tapers to a subpellicular granule (Fig. 1.14, C). Upon discharge (Fig. 1. 

 14, D), the positions of these components are reversed, the trichocyst- 

 granule adhering to the pellicle (81). Discharge apparently involves turn- 

 ing the trichocyst inside out. 



Trichocysts have been interpreted as offensive and defensive weapons 

 and as organelles of attachment. Under artificial stimulation, trichocysts 

 of Entorhipidium pilatum are often expelled from the body but they 

 sometimes backfire into the endoplasm (148). Therefore, the behavior of 

 trichocysts under artificial conditions should be interpreted cautiously. A 

 protective function is often suggested but has not been adequately dem- 

 onstrated in Paraynecium. Another suggestion for Paramecium (197) is 

 that the trichocyst, which hardens after extrusion so that only the tip 

 remains sticky, serves in anchoring the ciliates. The stimulus to natural 

 discharge, in which only a portion of the trichocyst is discharged, is said 

 to be contact with solid objects. In contrast to the trichocysts of Para- 

 ?7iecium, those of Dileptus gigas apparently are offensive and defensive 

 weapons. They paralyze some organisms, induce cytolysis of others, and 

 cause vigorous reactions in additional Protozoa (215). Paralysis of flagel- 

 lates and small ciliates is produced by trichocysts of Dileptus anser, and 

 even large rotifers react vigorously (81). Contact of rotifers with the 

 tentacles of Actinobolina vorax also may be followed by paralysis (225). 



Trichocysts have been reported in various flagellates (77). Two types 

 have been described in Gonyostominn (Fig. 1. 14, B) — spindle-shaped 

 trichocysts and small spherical ones, both distributed in the cortex. The 

 former become long filaments when discharged; the latter give rise to 

 short delicate filaments (21). The "trichocysts" of Chilomonas, repre- 

 sented by refractile bodies lining the pharyngeal groove, are discharged 

 as long slender threads. Another type, possibly represented by small 

 cortical inclusions, gives rise to short thin filaments. Filamentous struc- 

 tures also have been interpreted as discharged trichocysts in species of 

 Polykrikos, Peridinium, Diplopsalis, and Ceratium (142). 



