42 BEHAVIOR OF THE LOWER ORGANISMS 



body is slender but blunt, the posterior part thicker, but more pointed. 

 Thus the two ends differ, as in some bacteria, and there is a further 



Flo. 31. Examples of ciliate infusoria. a, Spirostomum ambiguum Ehr., after Stein. 

 b, Stentor rieselii Ehr., after Stein, c. Vorticetta nebulijera. O. F. M., after Butschli. d, Col- 

 pidium colpoda Ehr., after Schewiakoff, from Butschli. e, Loxophyllum meieagris O. F. M., 

 after Butschli. /, Stylonychia mytilus Ehr., after Engelmann. 



differentiation of the lateral surfaces. One side, the oral surface, bears 

 a broad, oblique groove, known as the oral groove, or peristome, ex- 



