288 THE DEVELOPMENT OF PROTOZOA. 



possess of knowing to what species an embryo belongs is either 

 to see it at the time of its birth, or watch it until it has grown 

 to an adult condition. The former is a comparatively easy task ; 

 but the latter has as an obstacle to such a consummation the 

 element of time, and the difficulty of keeping such minute 

 creatures in view, and alive, for any considerable period. 



The young of Stentor passes through a series of changes 

 which differ in some respects from those of Paramecium ; for 

 instance, it begins as a simple globule, and then develops within 

 it a single, globular, contractile vesicle ; but neither in the next 

 phase, nor at any time, are there to be seen such globe-tipped 

 cilia as are so conspicuous on the young Paramecium. At the 



time of its birth the embryo Stentor (fig. 

 189) possesses two sets of vibratile cilia, 

 which are disposed in such a manner as to 

 give it a strong resemblance to some of the 

 Protozoans of a lower rank, e. g\, Pleuro- 

 nema (p. 170, fig. 99) ; and in fact the shape 

 and proportions of its body are such that 

 one could hardly be persuaded that it had the most distant rela- 

 tionship to its parent, were it not possible to see that it possesses 

 these characters before it is born. Of its two kinds of cilia, the 

 smaller are spread universally over the body in longitudinal lines, 

 and the others, possessing more of the character of lashes, are 

 disposed in a very oblique, arched line, (fig. 189, rf,) which ex- 

 tends, from near the anterior end of the body, backwards, first 

 toward the left side, and then transversely along the lower face 

 to a point a little to the left of the middle line, where it termi- 

 nates abruptly. The space embraced by this arch corresponds to 

 the disc of the adult, (fig. 30, 5,) but as yet it lies nearly in the 

 same plane with the rest of the body, like the homologous region 

 of the most oblique, adult forms of this group. In progress of 



Fig. 189. The embryo of Stentor poly morphus. Ehr. 350 diam. A view 

 of the inferior side of the body. A, the anterior, and P the posterior end ; e?, the 

 semicircle of vibratile cilia at the edge of the disc ; cv, the contractile vesicle. 

 From Claparede. 



