PHYLUM PROTOZOA 63 



There are four orders: (i) HOLOTRICHA, (2) HETEROTRICHA, 

 (3) HYPOTRICHA, (4) PERITRICHA. 



Order i. Holotricha (Figs. 33 and 42). CILIATA with cilia 

 all over the body and of approximately equal length and thick- 

 ness. Examples: -Paramecium (Fig. 33), Coleps (Fig. 42, A), 

 Loxophyllum (Fig. 42, B), Colpodq (Fig. 42, C), Opalina (Fig. 

 42, D). 



The HOLOTRICHA are probably the most primitive INFUSORIA. 

 Paramecium caudatum is>the best known species. Members of 



FIG. 42. INFUSORIA of the order HOLOTRICHA. A, Coleps hirtus. B, Loxo- 

 phyllum rostratum. C, Colpoda cucullulus. D, Opalina ranarum; a, macro- 

 nuclei. (A, B, C, from Conn; D from Lankester, after Zeller.) 



the following genera are frequently found in fresh- water cultures: 

 Coleps (Fig. 42, A), Loxophyllum (Fig. 42, B), and Colpoda 

 (Fig. 42, C). Opalina ranarum (Fig. 42, D) is a large multi- 

 nucleate species living in the intestine of the frog. It has no 

 mouth, but absorbs digested foods through the surface. 



Order 2. Heterotricha (Fig. 43, A). CILIATA whose cilia 

 cover the entire body, but are larger and stronger about the 

 mouth opening than elsewhere. This adoral ciliated spiral con- 

 sists of rows of cilia fused into membranelles and leads into the 

 mouth. Examples: Spirostomum, Bursaria, and Stentor (Fig. 

 43, A). 



