ZOOL.— Vol. III.] STEVENS— CILIATE INFUSORIA. 7 



agents. The ectoplasm is clearly marked only at the 

 margin of the attachment disc, between its cuticula and 

 fibre layers, and within the triangular basal portion of the 

 oral band, where it is either homogeneous or very finely 

 granular (fig. 9, s^). The entoplasm is coarsely alveolar 

 in both discs and more finely alveolar in the neck. 



Oral Disc. — The oral disc is irregularly circular in out- 

 line, having a projection on the left side opposite the buccal 

 cavity (fig. 3). The ventral side is depressed centrally 

 and posteriorly (fig. 3); the dorsal side convex laterally 

 and posteriorly,^ but continuous with the neck anteriorly 

 (fig. 2). The width of the disc varies from 33.5 /^ to 57 /x 

 in fixed material, and was 72 ytt in the large living specimen 

 cited above (fig. 69). 



The mouth and pharynx form a pear-shaped cavity 

 extending obliquely nearly three-fourths of the width of 

 the body, its greatest width being about three-fifths of the 

 length. The external opening, generally oval, is very 

 variable in form and size in the living animal, as indeed 

 are the whole mouth and pharynx. The lower lip is merely 

 a transparent fold of pellicula, while the upper lip is made 

 thick and heavy by the ciliary band which twists and passes 

 under it to form the roof of the pharynx (figs. 3, 4 and 9). 



The oral ciliary band begins just above the pharynx on 

 the left side, curves about the posterior extremity and right 

 side, and passes with a twist under the upper lip of the 

 mouth, where it broadens out and covers the roof of the 

 pharynx into which its cilia descend (figs. 3, 4, 9 and 17). 

 The band is made up of about one hundred and twenty- 

 five transverse rows of fine long cilia which are usually 

 twisted together in action so as to appear under low power 

 as so many stout membranellas, but under Abbe homo- 

 geneous apochromatic oil immersion 1.5 mm., oc. 8, the 

 individual cilia are plainly seen in the living specimen, 

 hundreds of them in each row forming a flat brush or a 



1 1 have used the terms anterior and posterior vi\t\i reference to the orientation of the 

 animal when it swims: the attachment disc is almost alwaj's forward and is therefore 

 the anterior and the other the posterior end. 



