MORPHOLOGY 73 



Whether the numerous 12-20^ long needle-like structures which 

 Kahl observed in Remanella (p. 727) are modified trichites or not, 

 is not known. 



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 toxicysts. But Kruger 

 and Hayes (1938) found that the extruded trichocysts can be recog- 

 nized. 



Perhaps the most frequently studied trichocysts are those of 

 Paramecium. They are elongate pyriform, with a fine tip at the 

 broad end facing the body surface. The tip is connected with the 

 pellicle (Fig. 19, 0- Kruger found this tip is covered by a cap (Fig. 

 21, a) which can be seen under darkfield or phase microscope and 

 which was demonstrated by Jakus (1945) in an electron micrograph 

 (Fig. 22, a). When extruded violently, the entire structure is to be 

 found outside the body of Paramecium. The extruded trichocyst is 

 composed of two parts: the tip and the main body (Fig. 21, b). The 

 tip is a small inverted tack, and may be straight, curved or bent. 

 The main body or shaft is a straight rod, tapering gradually into a 

 sharp point at the end opposite the tip. Extruded trichocysts meas- 

 ure 20-40yu or more in length, and do not show any visible struc- 

 tures, except a highly refractile granule present at the base of the 

 tuck-shaped tip (Fig. 21, b). The electron microscope studies of the 

 extruded trichocysts by Jakus (1945), Jakus and Hall (1946) and 

 Wohlfarth-Bottermann (1950), show the shaft to be cross-striated 

 (Fig. 22). Jakus considers that the main component of the tricho- 

 cyst is a thin cylindrical membrane formed by close packing of 

 longitudinal fibrils characterized by a periodic pattern (somewhat 

 resembling that of collagen), and as the fibrils are in phase with re- 

 spect to this pattern, the membrane appears cross-striated. 



As to the mechanism of the extrusion, no precise information is 

 available, though all observers agree that the contents of the tricho- 

 cyst suddenly increase in volume. Kruger maintains that the tricho- 

 cyst cap is first lifted and the swelling body increases enormously in 

 volume by absorbing water and lengthwise extension takes place, 

 while Jakus is inclined to think that the membrane itself extends by 

 the sudden uptake of water. 



