EARLY ORIGIN OF THE OVA. 125 



notices that it seems improbable that they 

 would be correspondingly affected by subse- 

 quent modifications of parental structure. Of 

 course it is not certain that this is a valid 

 argument. We know that the paternal half of 

 the reproductive elements does not enter the 

 ovum till a comparatively late stage in its history, 

 and it is quite possible that maternal elements or 

 gemmules may also enter the ovum from without. 

 If reproductive elements were confined to one 

 special part or organ, we should be unable to ex- 

 plain the reproduction of lost limbs in salamanders, 

 and the persistent effect of intercrossing on subse- 

 quent issue by the same mother, and the propaga- 

 tion of plants from shoots, or of the begonia from 

 minute fragments of leaves, or the development of 

 small pieces of water-worms into complete animals. 



