350 Vniversitij of Calif ornia PuNications. [Zoology 



resembles more the deep pocket-like cavity of Bursaria trunca- 

 tella. The cavity is very much greater than is indicated by the 

 size of the triangular space on the ventral surface, for it is not 

 only wider, extending under the right adoral lip, but it is much 

 longer, extending down into the protoplasm as a large sac from 

 the left corner of which the short gullet arises. Biitschli ('89) 

 describes the right lip as lamella-like, bending around to form a 

 distinct angle and extending to the median line, while the left 

 lip is placed so that the peristome is Avide open but can be 

 changed by the contraction of the left side of the adoral zone. 

 The buccal incision is widest at the anterior end and narrowest 

 posteriorly. The opening between the right and left lip is va- 

 riable and depends on the state of contraction, for at times the 

 groove is wide open and at others the margins are closely approx- 

 imated. The relation of the length of peristome to the length of 

 the animal is also a variable quantity. Biitschli (^S9) says the 

 peristome is one-quarter or less of the length of the body. The 

 surface of the groove is entirely free from cilia, but on the outer 

 edge certain structures are found which compensate for the ab- 

 sence of cilia. Along the right side and emerging from the angle 

 formed by the right lip and adoral zone is the undulating mem- 

 brane, and along the anterior edge and down the left lip of the 

 buccal incision extending down into the gullet are the mem- 

 branellae. 



LOCOMOTOR MOVEMENTS. 



I. GLIDING. 



The animals spend most of the time on the floor or sides of 

 the aquarium and in the field are found most frequently on the 

 bottom of the sloughs amongst the zoogiea. The bacteria grow 

 rapidly and cover the bottom of the dish, forming a scum or coat, 

 over which the animals may be seen to glide in large numbers. 

 very few swimming freely in the w^ater. 



Gliding is a slow movement, interrupted with frequent stops. 

 It usually occurs on the bottom of the aquarium, more rarely on 

 the sides and surface film. It is the most common method of 

 locomotion, partly because of the specific gravity of the animal, 



