REPRODUCTION. 415 



by the aid of the microscope, through the transparent co- 

 vering; and while yet retained within the body of the pa- 

 rent, other still minuter globules are developed within these, 

 constituting a third generation of these animals. After a 

 certain period, the young, which have thus been formed, 

 escape by the bursting of the parent volvox, which, in con- 

 sequence, perishes. Similar phenomena are presented by 

 many of the Infusoria. In some of the Entozoa, likewise, 

 as in the Hydatid, the young are developed within the pa- 

 rent; and this proceeds successively for an indefinite number 

 of generations.* In most cases of the spontaneous evolution 



* The mode in which infusory animalcules are produced and multiplied is 

 involved in much obscurity. Many distinguished naturalists, adopting the 

 views of Buffon, have regarded them as the product of an inherent power 

 belonging to a certain class of material particles, which, in circumstances fa- 

 vourable to its operation, tends to form these minute organizations, and in 

 this manner they explain how the same organic matter which had composed 

 former living aggregates, on the dissolution of their union, reappears under 

 new forms of life, and gives rise to the phenomenon of innumerable animal- 

 cules, starting into being, and commencing a new, but fleeting career of ex- 

 istence. Yet the analogy of every other department of the animal and ve- 

 getable 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 disco- 

 veries of Ehrenberg relative to the organization of the Rotifera go far to- 

 wards 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 assumption 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 dia- 

 meter, they were distinctly seen to excite currents, and to swallow food. 

 The same diligent observer detected the young of the Rotifer vulgaris, per- 

 fectly formed, moving in the interior of the parent animalcule, and excluded 

 in a living state, thus constituting them viviparous animals, as the former were 



