GENESIS. 281 



physiological, such powers exist, — if, under fit conditions, 

 and when not much specialized, they manifest such powers in 

 a way as marked as that in which the contents of sperm-cells 

 and germ-cells manifest them; then, it becomes clear that 

 the properties of sperm-cells and germ-cells are not so 

 peculiar as we are apt to assume. Again, the organs 



emitting sperm-cells and germ-cells have none of the special- 

 ities of structure which might be looked for, did sperm-cells 

 and germ-cells need endowing with properties unlike those 

 of all other organic agents. On the contrary, these reproduc- 

 tive centres proceed from tissues characterized by their low 

 organization. In plants, for example, it is not appendages 

 that have acquired considerable structure which produce the 

 fructifying particles: these arise at the extremities of the 

 axes where the degree of structure is the least. The cells 

 out of which come the egg and the pollen-grains, are formed 

 from undifferentiated tissue in the interior of the ovule and 

 of the stamen. Among many inferior animals devoid of 

 special reproductive organs, such as the Hydra, the ova and 

 spermatozoa originate from the interstitial cells of the ecto- 

 derm, which lie among the bases of the functional cells — 

 have not been differentiated for function ; and in the Medusce, 

 according to Weismann, they arise in the homologous layer, 

 save where the medusoid form remains attached, and then 

 they arise in the endoderm and migrate to the ectoderm: 

 lack of specialization being in all cases implied. Then in 

 the higher animals these same generative agents appear to 

 be merely modified epithelium-cells — cells not remarkable 

 for their complexity of structure but rather for their sim- 

 plicity. If, by way of demurrer to this view, it be asked 

 why other epithelium-cells do not exhibit like properties ; there 

 are two replies. The first is that other epithelium-cells are 

 usually so far changed to fit them to their special functions 

 that they are unfitted for assuming the reproductive function. 

 The second is that in some cases, where they are but little 

 specialized, they do exhibit the like properties: not, indeed. 



