OF THE ALIMENTARY TRACT 201 



the head. The surface is entirely covered by diago- 

 nally longitudinal rows of fine cilia arising in grooves 

 in the ectoplasm. To one side of the anterior end is 

 a funnel-like depression, the peristome, leading into 

 the cytostome or mouth. The peristome is lined by 

 longer and more delicate cilia. These gather food 

 and by selection, or "taste" as Dobell (1921) ex- 

 presses it, pass on the desirable to be ingested through 

 the cytostome and short tubal gullet into the endo- 

 plasm, where it is digested in the vacuole stomachs. 

 The food consists of a variety of substances from the 

 intestinal contents and tissues of its habitat, the rec- 

 ognizable bodies being bacteria, starch granules, red 

 blood corpuscles, leucocytes and tissue fragments. 



The cytoplasm is mainly granular, alveolated and 

 vacuolated endoplasm, wdth a thin clear zone of ecto- 

 plasm beneath a membranous pellicle. 



The contractile vacuoles are tw^o in number, one 

 in the dorsal region, slightly anterior, the other near 

 the posterior end. They pulsate slowly and ryth- 

 mically and are not easily made out at all times. The 

 excretory pore is a small oblique aperture in the ter- 

 minal end. 



The macronucleus, a large body of kidney-like or 

 sausage-like shape, lies near the middle of the body 

 and in its bend is the minute micronucleus. In 

 stained specimens the chromatin of the macronu- 

 cleus is a mass of compact granules. The micronu- 

 cleus may be so closely in contact with the larger 

 nucleus as to be obscured. 



