CRITICISM OF Owen's theory. 321 



sion, gradually loses by dilution a portion of its plastic 

 force. If on starting it had a force of 1 00, after fifty sub- 

 divisions it will have no more than 2. It is this necessary 

 dilution of power in repeated reproductions which pre- 

 vents Parthenogenesis from being indefinitely prolonged. 

 Such is the theory, in every way remarkable, pro- 

 posed by our great anatomist ; and before proceeding 

 to examine its stability, I will adduce the strongest 

 illustration in its favour I have yet found. The theory 

 assumes that some of the original germ-cells are re- 

 tained 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 for- 

 merly seen that the germ-mass of the Eolis, Doris, 

 and Aplysia, normally develops itself into one, two, 

 tlu-ee, 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 in- 

 cluded in each distinct mass, and that it is the origin 

 of each embryo. Whether the cells are unchanged or 

 not, may be a question ; it is certain that they are in- 

 cluded : and as there can be little difference in the pro- 

 cess, 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. 



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