20 HERBERT SPENCER AND 



under ordinary conditions, would develop into a normal 

 larva or adult. 



Arguing from these observations, Driesch constructed 

 an epigenetic theory of development not very different 

 from Herbert Spencer's, and laid down the law that 

 the destiny of every cell in the embryo is a function 

 of its position. 



But before this R-oux had shown that if one of the 

 first two blastomeres of a frog's egg is destroyed, the 

 result is, not the formation of a whole embryo of half 

 size, but a half embryo, and further observation and 

 experiment has shown that in whole classes of the 

 animal kingdom the materials necessary for the forma- 

 tion of the different organs of the larva and adult that 

 is to be are already present and localized in the germ- 

 cell, and are dealt out, according to their kind, at every 

 division from the first onwards. 



Here I must digress for a moment to explain that 

 Weismann, agreeing in this matter with Strasburger and 

 O. Hertwig, held it as proved that the biophors and the 

 aggregates of biophors forming determinants, are located 

 in the chromosomes of the nucleus of the germ-cell. This 

 view, supported by a number of considerations, seemed 

 to be amply proved by an experiment of Boveri, who 

 fertilized the anucleate fragments of the eggs of one 

 species of sea-urchin with the sperm of another species, 

 and reared larvae which exhibited the paternal characters 

 only. But these results have since been called into 

 question and have quite recently been contradicted by 

 the experiments of Kupelwieser and Loeb, who fertilized 

 the ovum of a sea-urchin with the spermatozoon of 

 a mollusc, and obtained the characteristic larva of the 

 sea-urchin without any trace of paternal characters. 

 And numerous other experiments — too many for me tO' 

 recount now — have shown that, whatever may be the 

 exact role of the nucleus, the cytoplasm of the germ-cell 

 certainly contains organ-forming materials, and that if 



