VORTICELLA. 11 



end of the vestibule, extending deep into the 

 endosarc. 



i. The anus is a small opening into the vestibule, 

 visible only at the moment of extrusion of fsecal 

 matter. 



g. The cilia are arranged in an incomplete ring round 

 the margin of the disc, in the groove between the 

 disc and peristome : they also line the vestibule 

 and pharynx. They produce a current which 

 runs round the disc in the direction opposite to 

 that of the hands of a watch, then down the 

 vestibule near its ventral surface, and, after a 

 turn in the upper part of the pharynx, up along 

 the dorsal wall of the vestibule to the exterior- 

 There is a long undulating membrane projecting 

 through the external opening. The cilia serve 

 to sweep food particles into the interior of the 

 animal. A circular line near the attached end 

 of the body marks the zone from which the aboral 

 cilia will develop during fission. 

 * h. Food-vacuoles, enclosing food particles, may often 

 be seen circulating in the endosarc. 



i. The pulsating vacuole is a spherical cavity, situated 

 between the disc and the vestibule, and opening 

 into the latter. It pulsates rhythmically. 



k. The mega-nucleus is an elongated curved rod lying in 



the endosarc, about the middle of the body. 

 1. The micro-nucleus is a minute corpuscle applied to 



one side of the mega-nucleus. It can only be 



demonstrated on well-stained preparations. 

 m. ' Myonemes ' are developed in the deeper layer of 



the ectosarc, especially at the proximal end of 



the body, close to the stalk. 

 2. The stalk. 



a. The pellicle forms a thick covering to the stalk : 



to its elasticity the straightening of the stalk 



after contraction is probably due. 



