THE ORIGIN OF VARIATIONS 55 



process furnishes an inexhaustible supply of fresh 

 combinations of individual variations." ^ 



We owe to Dr. Vernon a recent and careful con- 

 sideration of the evidence in favour of these two 

 factors. Amphimixis we have ah'eady rejected as a 

 cause of progressive variations — variations away from 

 the specitic type — though it may be a cause of re- 

 gressive variations — back to the type. Dr. Vernon, 

 however, accepts the teaching of Weismann on this 

 point, but it is probably not necessary here to re- 

 consider the evidence which he advances. 



It is of importance, however, carefully to consider 

 the evidence in favour of the view that the ultimate 

 cause of variations is to be found in inequalities of 

 nutrition acting on the individual constituents of the 

 germ-plasm. Dr. Vernon conducted a long series of 

 experiments on the sex-cells of the sea-urchin, known 

 to systematists as Strongylo-centrotus lividus. The 

 ova, or the spermatozoa, or both, were kept for 

 varying numbers of hours in sea-water before fertili- 

 sation was allowed to occur ; and after eight days the 

 larvae resultiui^f from the fertilisation were measured. 

 It was found, in brief, that differences in the degree 

 of freshness of these gametes, that is to say, "in- 

 equalities of nutrition acting on the germ-plasm," 

 had " a very appreciable effect upon the size of the 

 subsequently developing larva\" The efiects differed 

 markedly according as whether the female or the 

 male gametes, or both, were stale or fresh ; whence it 

 may be inferred that different portions of the same 

 sex-cell may also react differently to one and the 



1 I quote from the excellent chapter, " Blastogeinc Variulions," 

 in Dr. H. M. Vernon's " Variations in Animals and Plants." (Inter- 

 national Scientific Series, vol. Ixxxviii.) 



