THE INFUSORIA 



201 



(Entz, Maupas). This view will be more appropriately examined in 

 connection with the Suctoria. 



The Holotrichida appear to be the most generalized of the entire 

 group of Infusoria, but a few forms among them have a slight regional 

 differentiation of cilia suggesting the characteristics of the Heterotri- 

 chida (Z>7#^7/.s-, Pleuronema, Ophryoglena, etc.). In fact, there appears 

 to be no sharp line between the two divisions, although the presence 

 of an adoral band of cilia in the Heterotrichida is a sufficient differen- 



Pig. 113. Illustrating Butschli's hypothesis of the origin of the Hypotrichida. [BiJTSCHl.l.] 



A. Stephanopogon colpoda Entz. B. Peritromus emmce St. C. Onychodromus grandis St. 

 c, cirri. 



tial. In some forms the uniform coating of cilia is broken in certain 

 regions, giving characteristic girdled forms, which are included as a 

 separate order apart from the Holotrichida by some writers (Haeckel). 

 In the Holotrichida, also, there are a few forms which show a distinct 

 tendency toward bilateral symmetry, due primarily to a bending of 

 the body, and followed by a reduction of the cilia upon the arched 

 side (Stephanopogon, Fig. 113, A). Biitschli derives the Hypotri- 

 chida from the Heterotrichida by the supposition of the loss of cilia 

 upon the arched dorsal side and incomplete closure of the adoral ring 



