592 THE REPRODUCTIVE FUNCTIONS. 



taneous evolution of gemmules within the parent, 

 channels are provided for their exit ; but the 

 gemmules of the Actinia force their way through 

 the sides of the body, which readily open to give 



and commencing a new, but fleeting career of existence. Yet 

 the analogy of every other department of the animal and vege- 

 table kingdoms is directly opposed to the supposition that any 

 living being can arise without its having been originally derived 

 from an individual of the same species as itself, and of which it 

 once formed a part. The difficulty which the hypothesis of the 

 spontaneous production of infusory animalcules professes to 

 remove, consists in our inability to trace the pre-existence of the 

 germs in the fluid, where these animalcules are found to arise ; 

 and to follow the operations of nature in these regions of infinite 

 minuteness. The discoveries of Ehrenberg relative to the orga- 

 nization of the Rotifera go far towards placing these diminutive 

 beings more on a level, both in structure and in functions, with 

 the larger animals, of whose history and economy we have a 

 more familiar and certain knowledge ; and in superseding the 

 hypothesis above referred to, by showing that the bold assump- 

 tion on which it rests, is not required for the explanation of the 

 observed phenomena. In many of these animalcules, he has 

 seen the ova excluded in the form of extremely minute globules, 

 the 12,000th of an inch in diameter. When these had grown 

 to the size of the 1700th of an inch, or seven times their original 

 diameter, they were distinctly seen to excite currents, and to 

 swallow food. The same diligent observer detected the young 

 of the Rotifer vulgaris, perfectly formed, moving in the interior 

 of the parent animalcule, and excluded in a living state ; thus 

 constituting them viviparous animals, as the former were ovi- 

 parous. Other species, again, imitate the hydra, in being what 

 is termed gemmiparous, that is, producing gemmules (like the 

 budding of a plant), which shoot forth from the side of the 

 parent, and are soon provided with cilia, enabling them, when 

 separated, to provide for their own subsistence; although they 

 are of a very diminutive size when thus cast off. 



