PROTOZOA 



81 



the opposite end of the body (Fig. 46). By coalescence along 

 such rows, usually in the neighborhood of the mouth, undulating 

 membranes are formed. By coalescence of two or more trans- 



Fig. 46— FRONTONIA LEUCAS 



A typical ciliated protozoan with cilia distributed uni- 

 formly about the body. It has a large mouth through 

 which diatoms are taken in. c, one of the canals run- 

 ning to the contractile vacuole, v; N, macronucleus; 

 n, micronucleus 



From a drawing by Schcwiakow 

 Magnification, 190 



WW- !••<'/ wi-, ■•-m 



verse rows in the region of the mouth, pyramid-shaped organs, 

 called membranelles, are formed; these are active in food-getting. 

 Since these organs are always present in a curved row leading to 

 the mouth, the aggregate is spoken of as the adoral* zone of 

 membranelles, or more simply as the adoral zone. Other coal- 

 esced cilia may be found on various parts of the ventral surface. 

 These are usually circular in cross-section and are known as 

 cirri* (singular, cirrus), specially designated as frontal cirri, ven- 

 tral cirri, anal cirri, and caudal cirri, according to their location. 

 Co-ordinating fibrils connect the bases of longitudinal and 

 transverse rows of cilia. Stimuli from the anterior end pass 

 down these fibrils, stimulating the cilia one after the other to 

 contract and resulting in a wave-like contraction of the ciliary 

 coating from the mouth to the opposite end of the body (Fig. 

 46). In many forms a mechanism resembling a simple nervous 

 system is present. In Euplotes patella, for example, fibrils from 

 the posterior anal cirri meet at the anterior end of the body in a 

 structure called the motorium, and from this another fibril makes 

 a circuit of the adoral membranelles ( Fig. 47 ) . By means of such 

 mechanisms the various activities of the cilia and cilia combina- 



* Adoral, from ad, near, and oral, mouth — near the mouth. 

 t Cirri, from the Latin cirrus, meaning a curl, a ringlet. 



