464 HEREDITY AND DEVELOPMENT 



these and other alleged advantages of the theory are real ad- 

 vantages. Does the theory clarify our conception of inherit- 

 ance ? and does it suggest experimental work, on which, 

 after all, we must base our conclusions as to these abstruse 

 questions ? Do the advantages of the theory outweigh the 

 difficulties ? 



The chief difficulties are (i) in the argument that the struggle 

 will work out in a discriminate selection, and (2) in the postulate 

 that a slight advantage gained by a set of determinants will 

 be able to persist through a long series of cell-divisions, till the 

 sex-cells of the offspring are again matured. 



Objections. What we have stated above is not more than 

 an outline of a theory which Weismann has developed with 

 great subtlety and in great detail, and many objections may 

 occur to our statement of the theory which are well met in 

 the author's own presentation. 



1. It has been objected that the whole concept of germinal 

 selection is visionary and unverifiable. The point, however, 

 is : does this hypothetical construction enable us to interpret 

 the facts better ? does it harmonise with visible facts ? is it con- 

 sistent with what we know of the behaviour of observable 

 living units ? It seems to us that an affirmative answer may 

 be given. The concept deals with an invisible world, but it 

 helps us to interpret such facts as the dwindling of useless parts, 

 the excessive growth of more or less indifferent structures 

 (such as some of the ornaments of shells), and in general the 

 frequent definiteness of variation. 



2. It may be objected that we can hardly think of invisible 

 bodies such as determinants struggling for food. But why 

 not ? Size seems an irrelevant consideration. Cells which are 

 invisible to the naked eye are seen under the microscope strug- 

 gling for food. The germ-cells in the ovary of Hydra devour 

 one another just as really as the embryos of the dog-whelk in 

 their egg-capsules on the sea-shore, just as really as the locusts 



