22 CALIFORNIA ACADEMY OF SCIENCES. CProc. 3D Ser. 



to its host when at rest. The animal has never been seen 

 to swim with the oral end forward, but moves backward 

 with a slow whirling motion in a slightly serpentine course, 

 with slight flexions of the oral end of the body. 



In other forms, where the infusorian swims with the 

 aboral end forward, a "Mundnaht," such as is present in 

 Dasytricha (Schuberg), indicates, according to Biitschli, 

 the path of migration of the primitive mouth from the ante- 

 rior to the posterior end. There is no indication of such 

 migration in Boveria. The several rows of body cilia all 

 extend in slightly converging lines from their juncture with 

 the outer row of oral cilia to the central bare space on the 

 aboral end. The direction of movement is therefore to be 

 explained as a modification due to environment. The con- 

 tinual movement of the cilia with the strong stroke forward 

 backs the animal up against the lining epithelium of the 

 tube in which it lives in such a way as practically to insure 

 it a radial position, as fixed as though it were attached to 

 the wall; and the same kind of ciliary motion serves all 

 ordinary purposes of food-getting and locomotion. In live 

 cultures it is often seen attached to small masses of cells 

 from the respiratory tree, by its basal cilia. 



The mouth and pharynx are very variable in size, and 

 the pharynx appears not to be permanent. When the ani- 

 mal is actively feeding, it is quite broad and deep, bending 

 slightly to one side, but at other times it is not evident in 

 the living infusorian, and it is rarely seen in sections (figs. 

 33 and 47). Various appearances of the peristomal region 

 are shown in figs. 32, 33 and 83. In the latter appear- 

 ance, which is very common when the infusorian is attached 

 and feeding, the elevated portion is thin, concave, and 

 nearly transparent. 



A large circular contractile vacuole is located at the oral 

 end immediately below the peristome. Its period varies 

 from 50 seconds to 9 minutes, 35 seconds, averaging 2-3 

 minutes. Its relation to the peristome and form when dis- 

 charging is shown in figs. 32, 48 and 49. 



