PROTOZOA AS CELLS 55 



osmium or tungsten used in the preparation of electron-micro- 

 scope specimens, (2) the regular ordering of these groupings 

 according to a crystalline pattern, and (3) apparently a considerable 

 volume increase most easily attributable to water uptake; 

 discharged trichocysts may be six to ten times as long as resting 

 ones, and probably not correspondingly more slender. 



The tip of the trichocyst of Paramecium is preformed in the 

 resting state and discharged without alteration. It is an elongate, 

 tack-shaped structure that does not flatten during drying and has 

 a striation period of 17 to 30 m/x. Species of Paramecium differ 

 consistently in the shape and size of the tip. In Frontonia the tip 

 is elliptical, unstriated, and of low density, and trichocysts of 

 some other ciliates apparently lack specialized tips. 



In a peculiar small phytoflagellate of uncertain (dinoflagellate 

 or cryptomonad) affinities, Oxyrrhis marina, Dragesco found 

 slender trichocyst bodies arranged peripherally. On discharge 

 these appeared as discrete fibers with a pronounced period of 

 60 m/x, resembling thin versions of the Paramecium rod. 



The toxic trichocysts of 24 species of gymnostomes studied by 

 Dragesco all are remarkably similar in morphology. In the intact 

 cell viewed with the light microscope they are found anywhere 

 around the periphery but most abundantly about the mouth; 

 they are visible as elongate, banana-shaped bodies. On discharge 

 they are visible in electron micrographs as flattened, empty 

 capsules and long, slender, unstriated shafts. Occasionally the tip 

 of the shaft appears thicker, and the author suggests that in this 

 type of trichocyst a preformed tubule within the resting capsule 

 is everted during discharge, incomplete eversion resulting in the 

 thicker terminal segment. 



Explosive trichocysts in the cryptomonad flagellate, Chilomonas 

 Paramecium, come in two sizes; large ones grouped about the 

 anterior pharyngeal invagination and smaller ones on the general 

 body surface. The latter appear in electron micrographs of dried 

 preparations to consist of two uniform fibers with an irregular, 

 bulbous, apical swelling from which a short, tapering twig 

 emerges at an angle. Pharyngeal trichocysts are similar but longer, 

 with several axial fibers. 



In addition to the true explosive trichocysts, many protozoa 

 possess mucigenic bodies, small globular elements typically 



