944 



PROTOZOA AND OTHER ANIMALS 



synonym of the former and Ladopsis Cheissin of the latter. According 

 to Jarocki (1934), the points of distinction are the shape of the macro- 

 nucleus, the size and position of the micronucleus, and the position of 

 the contractile vacuole. Whether such points are sufficient for distinction 

 of genera is questionable. 



The power of attachment, achieved by a sucker-like organelle, is 

 marked (Fig. 201D). Miyashita (1927) found that Ptychostomum 

 tanishi, when observed in the dissected-out gut, was in part attached to 

 the inner surface of the intestine and in part swam freely in the fluid. 



Figure 201. Ptychostomidae. A, Ptychostomum rossolimoi from Li?nnodrilus iiewaensis ; 

 B, skeletal fibrils of the sucker area of that species ; C, Ptychostomum chattoni from 

 Lumbriculus variegatus ; D, Pt. chattoni adherent by sucker to the intestinal wall of the 

 annelid. (A, B, after Studitfeky, 1930; C, D, after Rossolimo, 1925.) 



When put into water, the ciliates eventually attached themselves to sur- 

 faces. Heidenreich (1935) described strong attachment by the sucker 

 in P. rhynchelmh, folds of the intestinal wall being drawn into it. Beers, 

 however, remarked that in H. eheniae the sucker appears to be only 

 weakly functional, and most specimens were swimming freely in the 

 lumen of the intestine. In relation to the sedentary position, there is more 

 or less marked dorsoventral flattening of the elongated body. 



According to Studitsky (1930), the first step in the development of 

 the fixation apparatus is represented by the horseshoe-shaped, non- 

 ciliated area in the anterior part of the ventral surface of Ptychostomum 

 saenuridis, in which no skeletal structures have been described. The next 



