THE INFUSORIA 



2OI 



{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^w?/.y, 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- 



Fig. 113. Illustrating Butschli's hypothesis of the origin of the Hypotrichida. [BUTSCHU.] 



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

 ^, 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 (StepJianopogon, 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 



