188 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



1956c) is composed primarily of protein. Light microscopy 

 reveals converging fibrils and a cluster of vesicles in the cell at 

 the point of origin of the stalk. In electron micrographs, these 

 vesicles are seen to be rather thick- walled, vase-shaped "glandules" 

 embedded in the cytoplasm and opening into the cavity of the 

 stalk. The contents of the glandules, probably shrunken during 

 preparation, are dense and amorphous but are prolonged into the 

 stalk as discrete, dark fibers with a diameter of 60 to 120 m/x. In 

 the cytoplasm around the glandules are numerous, very dense, 

 spheroidal bodies that conceivably represent precursors of the 

 protein stalk secretion. Below a protoplasmic lip surrounding 

 the origin of the stalk, its surface appears to be formed by a 

 coalescence of peripheral fibers, with a dense, serrated external 

 layer. Fibers within the stalk are rather closely packed, with 

 interconnecting strands that may represent a precipitated matrix 

 material. 



These observations are of particular interest inasmuch as they 

 demonstrate the existence and the morphology of a specialized 

 secreting organelle in a protozoan cell. The glandules are totally 

 different from the structures from which stalks in some other 

 ciliates (e.g., peritrichs, see below) take origin. The authors cite 

 their unpublished data, however, to the effect that certain gymno- 

 stomes believed to be the closest relatives of chonotrichs accom- 

 plish temporary attachment by means of adhesive strands secreted 

 in simple glandules resembling those of Chilodochona. 



Order Trichostomatida 



In a speculative scheme of ciliate phylogeny, Corliss (1956) 

 recognized the Order Trichostomatida as a polyphyletic assem- 

 blage and placed it on the highway leading from gymnostomes to 

 hymenostomes; all other orders thus far considered occupied 

 side roads. In more recent studies (1958, 1961) he concludes that 

 the pivotal hymenostomes more probably arose from certain 

 gymnostomes and that the trichostomes constitute instead one 

 or more culs-de-sac. Be that as it may, certain trichostomes 

 exemplify with beautiful clarity the ontogenetic progression from 

 primitive gymnostome-like young to highly differentiated adult 

 forms (see Faure-Fremiet, 1950) and as such invite critical electron- 



