The Life History of Tillina Magna 387 



posterior region is easily recognized by the presence of a highly 

 characteristic lobe-like process of the dorsal surface, in which 

 lies the contractile vacuole, and which extends out beyond the 

 body proper on all sides, especially at the right posterior edge, A 

 continuation of this edge is extended along a depression on the 

 left side and ventrally into the peristomial region, and appears 

 finally as a tongue-like ridge lying on the floor of the pharynx. 

 This tongue gradually diminishes in width, and disappears near 

 the inner end of the pharynx. While the body in general is com- 

 posed of colorless protoplasm, pigmentation is found only in this 

 posterior lobe, which normally is filled with a mass of black gran- 

 ules. These granules are present when the young individuals 

 break away from the cyst, and cause the lobe to stand out in sharp 

 contrast from the main portion of the body, which at this time is 

 without food vacuoles, and is practically colorless. The lobe is 

 somewhat similar to that described in Colpidium colpoda. It 

 differs in being much more developed, and in being found in the 

 posterior rather than the anterior region (Plate I, Fig. i). 



The mouth is situated on the ventral surface in the anterior 

 half of the body, and extends from the region near the middle line 

 out toward the left side, where the peristomial region runs into it. 

 According to Gruber, the peristome is lacking. This is a mistake, 

 I think, as in every individual the mouth is always in its central 

 position, with a definite peristome leading to it. There is no 

 vestibule; the mouth leads directly into a long tubular, curved 

 pharynx or oesophagus, relatively much longer than that of Col- 

 poda. The pharynx, with its ridge-like tongue, bends anteriorly 

 inward toward the right side of the body, then it turns sharply 

 toward the posterior region, and ends just below the nucleus, its 

 walls widening out like a funnel (Plate I, Fig. 2). 



The entire surface of the body is covered with many longitu- 

 dinal bands or striae, which indicate the insertion lines of the cilia. 

 The striae are arranged on the surface in a similar manner to that 

 described by Schewiakoff for Colpidium colpoda. On the dorsal 

 surface the lines pass from the anterior to posterior end in straight 

 parallel rows, bending toward the left posteriorly. On the ventral 

 surface, however, they converge about the mouth, which, accord- 



