204 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



from each basal body. At lease 14 to 16 sheets of fibrils may be 

 counted within the kinetodesmos in some micrographs. Some 

 species oiCondylostoma are rather markedly contractile (Villeneuve- 

 Brachon, 1940). 



An interesting sidelight on ciliate differentiation is provided by 

 the observations of Pautard (1959a, 1959b) on the occurrence of 

 hydroxyapatite — the inorganic phosphate compound that is 

 deposited on collagen during the mineralization of vertebrate 

 bone — in Spirostomum ambiguum. As soil-based cultures of this 

 species age, over a period of months, hydroxyapatite appears in 

 small, beaded ossicles which later enlarge and fuse to form plates 

 in organisms from very old cultures. The ossicles are seen in thin 

 sections as a network of loosely connected islands, 1 to 3 /x in 

 diameter, below the basal bodies, generally along the meridional 

 lines. Spirostomum in these cultures, some weeks after inoculation, 

 engages in mass burrowing activity, mining the soil (in which 

 organic food is embedded) to a depth of centimeters. This 

 apparently occurs after exhaustion of food in the supernatant fluid. 

 Pautard suggests that hydroxyapatite serves a double function in 

 these ciliates as in vertebrate bones — as an articulable skeleton 

 providing support during tunneling activities and as a mineral 

 bank from which phosphate can be withdrawn for metabolic 

 needs, especially during the active "muscular" movements of 

 tunneling. 



Nyctotherus ovalis is a large heterotrich symbiotic in the cock- 

 roach gut. Its peristomal area is elongate and bears an adoral zone 

 of membranelles subtended by a thickened ectoplasmic band. 

 The membranelles continue into the deep peristomal tube leading 

 to the cytostome. The ectoplasmic band extends past the cyto- 

 stome and, now lacking cilia, up the opposite wall of the 

 peristome. Somatic cilia arise singly or in pairs from more or less 

 deep furrows. Electron micrographs show that the ectoplasm 

 within the ridges is extensively vacuolated. Beneath, at the level 

 of the kinetosomes, is a tangled network of randomly oriented 

 fine filaments (about 7 m/x in diameter). The kinetosomes bear 

 root fibrils that appear to emerge axially and pass medially; no 

 connections with the ectoplasmic network or any other structures 

 were observed. One micrograph shows neatly parallel tubular 

 fibrils perpendicular to these roots, at a deeper level, but their 



