CILIATES 189 



microscope scrutiny. Unfortunately, work on typical species has 

 not progressed far enough to justify inclusion here. 



The only trichostome for which limited electron-microscope 

 data are available is hotricha, representative of a family living 

 symbiotically in the rumina of ungulate mammals. Bretschneider 

 (1950) and Noirot-Timothee (1958b, 1958c) have investigated the 

 peculiar layer that forms a distinct boundary between ectoplasm 

 and endoplasm, visible in living and stained cells in the light 

 microscope. Noirot-Timothee's electron micrographs show that 

 it is composed of two layers of very fine parallel filaments 

 (diameter not given). In all cases filaments in the two layers are 

 oriented perpendicular to each other. From the internal layers, 

 tracts of filaments pass inward and anastomose to form a net, like 

 a string bag, around the nucleus. This complex, called the 

 karyophore, appears to act as a nuclear suspensor. The boundary 

 layer separates a rather homogeneous, finely filamentous ecto- 

 plasm from an inclusion-filled endoplasm. On both sides of the 

 filamentous layer and along the fibers of the karyophore are seen 

 abundant, small, disc-shaped bodies, about 350 m/x in diameter, 

 apparently membrane-limited and filled with a variably dense 

 granular material. The filamentous layers, Noirot-Timothee 

 suggests, provide an elastic support for the body, which is notably 

 plastic but not contractile. 



Noirot-Timothee notes that the kinetosome structure in 

 hotricha is conventional, with a basally open fibrous cylinder 

 capped by a cupped diaphragm above which the axial granule and 

 the central ciliary fibrils appear. From the base of the kinetosome, 

 a short root fiber descends directly into the cytoplasm. 



Order Astomatida 



The Order Astomatida presently is something of a waste-basket 

 for symbiotic (mainly in annelids) holotrichous ciliates whose 

 lack of any mouth structure obscures their true affinities. Tricho- 

 stome, hymenostome, apostome, and thigmotrich relationships 

 have been recognized for various astomes in recent years, and 

 eventual abandonment of the order seems likely. Such a step is 

 favored by a current authority on the group, de Puytorac, who 

 has used the electron microscope to examine several species 

 (1952-1961b). 



xfl-ISRAPtY)* 



