398 EVENINGS AT THE MICROSCOPE. 



organ is usually presented to us in the animals of this 

 class, the contractile bladders are here very complex. 

 Each when distended is globular; and it is surrounded by 

 a number of others of much smaller dimensions, and of a 

 drop-like form, so set as to radiate around the principal 

 vesicle as a centre, the rounded portion of each in appa- 

 rent contact with the vesicle, and the slender extremity 

 running off as an attenuated point till lost to sight in the 

 sarcode. The main vesicles alternately become distended, 

 and suddenly contract to a point ; while the radiating cells 

 are continually varying in size, though in a less degree. 

 It is customary to describe the secondary vesicles as coming 

 into view at the instant of the contraction of the primary 



PARAMECIUM. 



one, and to suppose that the emptying of the one is the 

 filling of the other, but I have not been able to observe 

 this mutual relation satisfactorily made out. The smaller 

 as well as the larger vesicles are conspicuous from their 

 colourless transparency ; for the general sarcode of the 

 body, though pellucid, is only so in the same degree as 

 glass, slightly smoked; besides that its clearness is often 

 impaired by crowds of granules and minute globules. 



You ask what is that comparatively large oval body 

 attached by its side to one of the leaves of the plant. It is 

 the egg of some considerable Rotifer, probably JSuchlanis, 

 which is always glued to some filament or stem of a water- 

 plant. It may interest you to watch the progress of the 

 contained embryo, which you can readily do, since the egg- 

 shell is as transparent as glass, and the infant animal 

 already displays the movements of independent life. 



