ZooL.— Vol. III.] STEVENS— CILIA TE INFUSORIA. 23 



The nucleus is barely visible in the living animal as 

 a clearer oval central area of relatively large size (fig. 

 32, n^). 



In the proximal half of the body are usually seen several 

 large food vacuoles, each usually containing a single cell 

 from the host, a leucocyte or epithelium cell. Diatoma- 

 ceous food masses also occur. These vacuoles frequently 

 pass aborally beyond the nucleus, but are most numerous 

 in the proximal half of the body, and in the majority of cases 

 are confined to that part. 



Structure and General Biology. — Seen in sections (Her- 

 mann or Flemming fixation, iron-hsematoxylin and rubin or 

 ruthenium red), the whole body is covered with a delicate 

 homogeneous pellicula, beneath which, and always adhering 

 closely to it, is a dense, finely granular layer of ectoplasm, 

 in which are imbedded the oval, deeply-staining basal 

 bodies of both systems of cilia. These basal bodies are 

 clearly visible in life as strongly refringent points beneath 

 the pellicula (figs. 47, 48, 50, 51, h^, b''-) . No myonemes 

 can be distinguished, and no definite longitudinal contrac- 

 tion has been observed other than that necessary to produce 

 slight flexions of the body when attached. 



The entoplasm is distinctly alveolar, coarsely about the 

 nucleus and finely at both ends. Near the aboral end is a 

 much denser band, having the form of a concavo-convex 

 lens, with the concave side toward the nucleus. The 

 position and form of this dense area, visible in the living 

 aniraral as well as in sections (fig. 48), suggest that it may 

 have something to do with the animal's adherence to its 

 host, but further observations are necessary to establish 

 such a function. 



Macronucleus. — Centrally placed is a large oval macro- 

 nucleus with a definite membrane and coarsely granular 

 contents. The granules, stained by iron-heematoxylin, are 

 scattered over the inner surface of the nuclear membrane, 

 and are gathered in a more or less centralized mass, in 

 which a linin thread-work forms a basis for the granules 



