REPRODUCTION. 531 



within the parent ; and this proceeds successively 

 for an indefinite number of generations.* In most 

 cases of the spontaneous 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 them passage; after Mhich, the lace- 

 rated part soon heals. 

 i ) . 



* The mode in which infusory animalcules are produced and multi- 

 plied is involved in much obscurity. Many distinguished naturalists, 

 adopting tlie views of BufFon, have regarded them as the product of 

 an inherent power belonging to a certain class of material particles, 

 which, in circumstances favourable 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 animalcules, starting 

 into being, 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 in- 

 dividual of the same species as itself, and of which it once formed a 

 part. The difficulty which the hypothesis of the spontaneous pro- 

 duction 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 complexity of their organization, and the 

 constancy with which each species preserves its form, 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 assrimp- 

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

 served 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 



