2O4 Heredity and Environment 



but the general polarity, symmetry and before fertilization. But 

 these egg characters, like any other character of the female, were 

 probably determined by chromosomes derived from her father 

 and mother; if so they are Mendelian characters inherited by 

 the mother through her chromosomes and carried over to the 

 first filial generation, not as factors but as developed characters. 

 Such cases may be called "maternal inheritance" since the charac- 

 ters come only from the egg, or "preinheritance" since these egg 

 characters are developed before fertilization. (See pp. 113, 114.) 

 Share of Chromosomes and Cytoplasm in Heredity and Devel- 

 opment. It will be observed that the correlation between chromo- 

 somes and adult characters is different in kind from that between 

 the cytoplasm of the egg and adult characters; in the latter case 

 polarity, symmetry and pattern of localization are characters of the 

 same kind in the egg and in the adult, and the correspondence is 

 comparatively close ; in the former there is no correspondence in 

 kind between the chromosomal peculiarities and the peculiarities of 

 the adult. This fact suggests that the chromosomal organization 

 is more fundamental than that of the cytoplasm; the chromo- 

 somes contain the germplasm, the cytoplasm is the somatoplasm ; 

 the chromosomes are chiefly concerned in heredity, the cytoplasm 

 in development. 



E. THE MECHANISM OF DEVELOPMENT 



Development consists in the transformation of the oosperm into 

 the adult. What is the mechanism by which this transformation 

 is effected? There is progressive differentiation of the germ into 

 the developed organism but by what process is this differentiation 

 accomplished ? 



Many different processes are concerned in embryonic differ- 

 entiation. From the standpoint of the cell the most important of 

 these are (i) the formation of different kinds of substances 

 in cells, (2) the localization and isolation of these substances, 

 (3) the transformation of these substances into various struc- 



