CILIATES 207 



in addition a dorsal zone of membranelles, and in some, posterior 

 rows or tufts of membranelles occur. A cortical layer of cyto- 

 plasm encloses the nuclei, contractile vacuoles, and usually one 

 or several skeletal plates. Most of the body volume is occupied 

 by an endoplasmic sac, sharply demarcated from the cortical zone 

 in stained specimens, and leading via a tube called the esophagus 

 to the mouth and via a rectum to the anal pore. The body is 

 relatively rigid but the anterior expanded buccal cavity or peri- 

 stome, with its encircling adoral ciliature, can be retracted and 

 covered over by surrounding cytoplasmic lips. 



Several genera of the Family Ophryoscolecidae have been 

 extensively studied by both light and electron microscopy by 

 Bretschneider (1959, 1960) and Noirot-Timothee (1957, 1958a, 

 1960). The two authors are in general agreement on details of 

 ultrastructure but their interpretations of these data relative to the 

 light-microscope picture diverge somewhat — a fact explainable 

 not by any lack of scrupulous consideration on their part but by 

 the fantastic complexity of ophryoscolecid morphology. The 

 species they have considered, all from the rumina of cattle and 

 sheep, are not always distinguishable in electron micrographs, and 

 seem sufficiently similar in ultrastructure to be described together. 



At the surface of the ophryoscolecid body is a highly differen- 

 tiated cortical zone consisting of at least four layers (Fig. 86, 

 PL XXIV). (1) The outermost is apparently a unit membrane, and 

 often appears to bear a fine granulation or fuzz on its outer 

 surface. Beneath this is (2) a homogeneous, moderately dense 

 layer, irregularly traversed by low-density canals. Its thickness 

 varies widely with species and with body region, since its outer 

 border may be thrown into folds, regular ridges, or knobs. It 

 apparently is composed of a glycoprotein. Its inner surface is 

 relatively smooth or minutely furrowed to accommodate (3) an 

 underlying system of orderly, parallel, longitudinal fibers. Each 

 of these consists of 15-m/x tubular fibrils arranged in two rows of 

 two to four each, the bundle assuming a regular rectangular shape 

 in cross-section. Below these longitudinal fibers is (4) a layer that 

 varies in thickness from nothing to well over 1 /x. It seems to be 

 composed of a finely filamentous material arranged generally 

 transversely and interrupted at intervals by transversely oriented 

 fissures. 



