CRITICISM OF OWEN's THEORY. 325 



Aphis putting forth larvae, to an indefinite extent. The 

 "prolific force/' instead of diminishing, by Repeated 

 subdivisions of the cells, retains its primitive fertility. 

 Kyber kept a plant, with larval Aphides, in a room the 

 temperature of which was constant, and saw these 

 larv?e produce broods for four years without interrup- 

 tion ! Whereas, had the temperature varied, these 

 larvse would have manifested changes similar to those 

 observed in ordinary circumstances, when the lowering 

 of the temperature in autumn stops the production of 

 larvae, and induces that of perfect insects. We may 

 also refer to the observation of Sir J. G. Daly ell, who 

 kept a strohila for several years continually budding. 



A fourth and last objection is, that the Polypidom, 

 which produces both Polypes and Medusae by gemma- 

 tion, also jDroduces eggs which become Polypes, as every 

 one knows, and eggs which become Medusae, as I have 

 found ; yet, aftei^ one of these egg-capsules has been 

 developed on the Polypidom, the budding process con- 

 tinues as before. This would imply that the original 

 prolific force, when nearly exhausted, produced eggs, 

 and then, suddenly recovering its vigour, continued the 

 production of buds. Now, an oscillating force of this 

 kind cannot be accepted. 



Although I think Owen's theory must be abandoned, 

 it seems to me the best which has been ofi'ered — indeed, 

 the only one which goes deeper than a phrase, and rests 

 on definite conditions. The very definiteness of these 

 conditions enables them to be closely tested and con- 

 fronted with fact. The pregnant ideas contained in his 



