NATURE OF REPRODUCTION. 



679 



nized with certainty by their distinctive marks. They are not confined 

 to infusions of decaying material artificially or accidentally prepared ; 

 but many of them have their natural habitation in the clearest waters 

 of lakes, pools, marshes, running brooks, or the open sea. Certain forms, 

 originally included in this class, such as Rotifer, Stephanoceros, and 

 Floscularia, have been found to possess a more complicated structure 

 than the rest, and to belong properly to the class of worms; while their 

 mode of reproduction is sufficiently manifest from the fact that living 

 embryos, in process of development, are often to be seen in their interior. 



Fig. 218. 



RTYLONTCHIA MYTILITS; a fresh-water infusorium. 1. Unimpregnated. 2. Impreg- 

 nated, and containing mature eggs and two embryos. 3. Showing the form of the embryo. 

 Magnified 375 diameters. (Stein.) 



Finally, the ciliated infusoria themselves have been shown to repro- 

 duce their species by means of eggs, formed in special generative organs 

 and fecundated by union of the sexes (Fig. 218). This fact, first demon 

 strated by Balbiani, has been since confirmed, in many instances, by 

 Stein, Engelmann, 1 and Cohn ; 2 Balbiani and Stein together having 



Zeitsehrift fur Wissenschaftliche Zoologie. 

 Ditto. Band xii. p. 197. 



Leipzig, 1862, Band xi. p. 347. 



