OF PROTOZOA. 163 



will see, however, that this revolving matter must be a fluid, in 

 order to pass by the various organs which are in its midst. 

 What its mode of circulation really teaches, I will speak of 

 hereafter, when we have seen its operations in other infusorians. 

 The contractile vesicle (cv) is a simple, small, globular cavity, 

 in the very middle of the body, and half-way between the top 

 and bottom of the bell. It contracts three times in a minute, 

 without exhibiting anything of the vivacity which is noticeable 

 in many of the Infusoria, but simply lessens to an almost invisible 

 point, and then as moderately expands to its full rounded con- 

 tour. The reproductive organ (n) lies in a 

 half circle across the body, on the ventral 

 side, and at a little higher level than the HJ 

 contractile vesicle. Its tawny yellow color, 

 and worm-shaped figure, render it by far 

 the most conspicuous organ of the body. 



One of the closely allied kinds of Vor- 

 ticellae, a Zoothamnium, exhibits the ob- 

 liquity of the bell (fig. 104) much more 

 clearly than the Epistylis, and especially 

 so because I have drawn it as it appeared 

 in profile ; a position in which all of the 

 bell-animalcules show the greatest degree 

 of obliquity. 



As we pass to the next illustration, we 

 will take a glance at Stentor, (fig. 30,) 

 merely to observe that the obliquity of its 

 figure is very decided when compared with 

 that of Epistylis or Zoothamnium, and 

 most emphatically so when it is swimming 

 in a semi-expanded state (fig. 31). It will 

 also serve as an intermediate step in the 

 passage to the more oblique Infusorians, 

 such, for instance, as we have represented 



in this figure, (fig. 96,) a Paramecium. Fig. 9s. 



Fig. 96. Paramecium caudatum. Ehr. 340 diam. A view from the dorsal 



