ROTIFERA 



211 



The female is pear-shaped, the posterior end being the stalk. The 

 anterior end is flattened and forms the trochal disc. This is, in many 

 rotifers, bordered by a double ciliated ring, the velum, the outer part 

 of which (the cingulum) is the original velum and is composed of 

 stronger cilia. The inner is called the trochus. Between the two rings, 

 which are thus preoral and postoral respectively, is a ciliated groove 

 in which is situated the mouth. The velum in life gives the impression 



l-m-c 



cct^"^ 



fi.m.C' 



ecdu. 



Fig. 165. A, Side view, diagrammatic, from Shipley and MacBride, and B, 

 transverse section of a female rotifer. An. anus (cloaca! aperture); c.m.c. 

 circular muscle cell; cii. cuticle; D. dorsal; e. eye; ecdu. excretory duct 

 (nephridium) ; ect. ectoderm; int. intestine; l.m. longitudinal muscle; m. 

 muscle; od. oviduct; tc. trochus; V. ventral. Other letters as in Fig. 164. 



of revolving wheels, the reason for the scientific name of the group. 

 In Hydatina the cingulum forms a complete ring and the trochus is 

 reduced to a double transverse row of cilia ; in the groove between 

 them is situated a number of papillae on which are stifle cilia. The 

 posterior end is called the foot and it terminates in a pincer-shaped 

 appendage, on which open glands with a sticky secretion. By means 

 of this apparatus the rotifer can anchor itself in the intervals of its 



14-2 



