PROTOZOA AND OTHER ANIMALS 94*3 



step is the strengthening of this area by skeletal fibrils, consisting, first, 

 of a set of longitudinal fibrils, and second, of a set of fibrils crossing 

 these. In further development there is differentiation and strengthening 

 of the two systems. The skeletal fibrils form an irregular network in the 

 floor of the sucker. The sucker itself is a simple concavity in P. rossolimoi 

 (Fig. 201A, B) and some other species; sometimes there are a few rows 

 of cilia on an elevated area in its floor. In other species, probably more 

 advanced in the evolutionary series, the border of the sucker is a lip- 

 like elevation. In some forms the sucker is circular (P. tanishi), but 

 often it is pointed posteriorly (P. chattoni. Fig. 20lC) or has an opening 

 (P. wfzesniewskii) or indentation (P. elongata). In H. eheniae it is V- 

 shaped. 



Cheissin (1932) described myonemes in addition to the skeletal 

 fibrils. Heidenreich (1935) stated that the fibrils of the sucker, as de- 

 scribed by authors, are contractile, thus being not skeletal structures but 

 myonemes. Beers, however, found no myonemes in the species he studied, 

 and concluded that all the fibrils have a supporting function. P. rhyn- 

 chelmh has, Heidenreich stated, unlike other species, a skeleton in the 

 sucker. The sucker is bordered by two sickle-formed skeletal bows, form- 

 ing a ring open posteriorly, and each sickle is prolonged posteriorly in a 

 handle. The two handles form a canal, the neck of which is surrounded 

 by three or four myoneme bands. 



In Ptychostomidae the oral apparatus is situated at what has been 

 regarded as the posterior end. Beers described a shallow, transverse peris- 

 tomal groove, bordered by lips bearing cilia, and a small cytostome 

 leading into a short, tubular cytopharynx. He found no food vacuoles 

 and no ingestion of ink particles, and consequently concluded that the 

 mouth is non-functional. In this group of ciliates the feeding apparatus 

 is in process of reduction. It functions in some species, possibly together 

 with saprozoic nutrition; in others it has, though still present, little role 

 to play in nutrition. 



ASTOMATA 



The suborder Astomata is systematically heterogeneous, lacking phylo- 

 genetic unity, as Kahl (1934) remarked. Cepede (1910) himself noted 

 that fact. The group includes many forms that lack complete descrip- 

 tions. There is no systematic unity to be obtained by bringing together 



