No. 609] THE THEORY OF THE GENE, 535 



shown to be only deferred Mendelian inheritance trace- 

 able to the chromatin of the nucleus in which the char- 

 acters shown by the egg or the embryo, have already been 

 determined before fertilization by the chromatin of the 

 mother alone. In consequence the appearance of the 

 Mendelian ratio is deferred to a succeeding generation 



{E) Action of Genes during Emhryonic Development 

 versus their Distribution in Heredity 

 On several occasions I have urged the importance of 

 keeping apart, for the present at least, the questions con- 

 nected with the distribution of the genes in succeeding 

 generations from questions connected with the physio- 

 logical action of the genetic factors during development, 

 because the embryological data have too often been con- 

 fused in premature attempts to interpret the genetic data. 

 It has been urged that such a procedure limits the legiti- 

 mate field of heredity to a process no more intellectual 

 than that of a game of cards, for Mendelism becomes 

 notliin^u' hwt shuffling- and dealing out new hands to each 

 succcsvivo iicnciiiiion. My plea is, I fear, based largely 

 on ex]>e(lien(*y, which may only too easily be interpreted 

 as narrow-mindedness ; yet I hope to be amongst the first 

 to welcome any real contribution concerning the nature of 

 genes based on the chemical changes that take place 

 in the embryo where the products of the genes show their 

 effects. In fact I do not know of any other more direct 

 way in which we can ultimately hope to find out the nature 

 of the materials that we think of as genes in the germ 

 cells. 



But experience has shown, I think, that only too often 

 the embryological data have been used to interpret the 

 transmission data to the detriment of both subjects; I 

 regret to see the inevitable difficnltitv^ that nvo natural, at 

 present, to the field of embryoh^.uy thrust upon the other 

 subject, where the problem is eonii)aratively simple; and 



