184 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



sidered the prototype" of the Ciliata. Present evidence strongly 

 implicates them in the ancestry of trichostomes, chonotrichs, and 

 hymenostomes, at least. Thus some of the ultrastructural enigmas 

 of higher forms might be clarified by scrutiny of the simplest sorts 

 of gymnostomes. Unfortunately, only a few tantalizing bits of 

 information are yet available in published form, all from the Paris 

 laboratory of Faure-Fremiet and Rouiller. So far, this all concerns 

 the morphology of pharyngeal protein fibers that in the carnivorous 

 gymnostomes appear as an expansible circlet of rods known as 

 trichites, and in the herbivorous gymnostomes as a rigid pharyn- 

 geal basket. Rouiller, Faure-Fremiet, and Gauchery (1956d) show 

 that all of these fibers are firm and elastic, birefringent, and 

 composed of elementary fibrils aligned in a paracrystalline order. 

 The elementary fibrils have a diameter of 15 to 20 rmt, appear 

 tubular in cross-section, and are packed in evenly-spaced parallel 

 rows within each trichite, thus being reminiscent of the axostyle 

 fibrils of Grasses Pyrsonympha. They are not, however, contractile. 

 In the carnivorous Coleps hirtus the trichites are spaced in a 

 discontinuous cylinder around the buccal depression. A similar 

 picture, with some variation in the orderliness of fibril packing, 

 is reported for two species of Prorodon. The pharyngeal basket of 

 the herbivorous Nassula aurea contains 25 trichites, elliptical in 

 cross-section, composed of densely and very regularly packed 

 elementary fibrils (Fig. 77, PL XXI). From one side of each rod 

 a few rows of fibrils extend medially as a curved lamella ; on the 

 outer side the rods are united by a sheath consisting of loosely 

 arranged elementary fibrils, and from this in turn regular humps 

 or crests of the same composition protrude into the cytoplasm. 

 Here and there within the sheath local zones of orderly packing 

 are observed. The authors state that a more complicated sort of 

 basket is observed in Chlamydodon and in Dysteria. 



Order Suctorida 



The Order Suctorida is a compact group of ciliates characterized 

 by the absence of cilia in the adult stage and the presence of 

 tentacles used for the capture and ingestion of living prey. Two 

 types of tentacles may be present: prehensile ones capable of 

 attaching and holding large, active prey, and sucking ones 

 through which protoplasm of food organisms, or sometimes 



