8 Introductory Remarks 



of chance and the corresponding wastefulness in the 

 world of the living. But it is doubtful whether this 

 idea of the r61e of Mendelian factors is correct. The 

 facts of experimental embryology strongly indicate 

 the possibility that the cytoplasm of the egg is the 

 future embryo (in the rough) and that the Mendelian 

 factors only impress the individual (and variety) char- 

 acters upon this rough block. This idea is supported 

 by the fact that the first development — in the sea 

 urchin to the gastrula stage inclusive — is independent 

 of the nucleus, which is the bearer of the Mendelian 

 factors. Not before the skeleton or mesenchyme is 

 formed in the sea urchin egg is the influence of the 

 nucleus noticeable. This has been shown in the ex- 

 periments of Boveri in which an enucleated fragment of 

 an egg was fertilized with a spermatozoon of a foreign 

 species. If this is generally true, it is conceivable that 

 the generic and possibly also the species characters 

 of organisms are determined by the cytoplasm of the 

 egg and not by the Mendelian factors. 



co-ordinating principle outside the units themselves and superior to 

 them. If the units constitute the physicochemical basis of life, as 

 their authors maintain, then this controlling principle, since it is an 

 essential feature of life, must of necessity be something which is not 

 physicochemical in nature. In short these theories lead us in the final 

 analysis to the same conclusion as that reached by the neovitalists. 

 If we are not content to accept this conclusion we must reject the 

 theories." These last sentences do not exhaust all the possibilities, 

 since the writer is trying to show in this book that the widest accept- 

 ance of the chromosome theory of heredity is compatible with a con- 

 sistent physicochemical conception of the organism as a whole. 



