CRITICISMS OF OWEN's THEORY. 303 



by dilution a portion of its plastic force. If on starting it 

 had a force of 100, after fifty subdivisions it will have no 

 more than 2. It is this necessary dilution of power in 

 repeated reproductions which prevents Parthenogenesis from 

 being indefinitely prolonged. 



Such is the theory, in every way remarkable, proposed by 



our great anatomist ; and before proceeding to examine its 



stability, I will adduce the strongest illustration in its fivour 



I have yet found. The theory assumes that some of the 



original germ-cells are retained untransformed in the body of 



the Hydra and Aphis, which cells, in virtue of their original 



tendency, subdivide and develop into new animals. We have 



formerly seen that the germ-mass of the Eolis, Boris, and 



Aplysia, normally develops itself into one, two, three, and even 



eight distinct animals. As this takes place contemporaneously, 



and in the same chorion — as one egg actually divides into 



several embryos, by a simple process of subdivision in the 



germ-mass — I do not see how Owen's position can be denied, 



that here at least the offspring of the original cell is actually 



included in each distinct mass, and that it is the origin of 



each embryo. AVhether the cells are unchanged or not, may 



be a question ; it is certain that they are included : and 



as there can be little difierence in the process, whether 



the progeny of one cell be developed simultaneously as in 



the Doris, or successively as in the Aphis, the fundamental 



position seems secured. I say seems, because I do not 



really think it is, nor do I find myself able to accept 



Owen's explanation. 



Quatrefages and Siebold object to the name of Partheno- 



