54 



GENETICS 



Hereditary factors have been described and have re- 

 ceived the major share of attention in the preceding 

 pages. Environmental factors may upon occasion, 



CYTOLOGICAL 



________________ 



Deals with the origin and development of the individual 

 The new method of attacking heredity 



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IVDIASI.LVJ.S 

 FIG. 78. Any-side-up Diagram of Genetical Sciences. 



however, cause enormous modifications in somatogenesis 

 although the limits of variation are set by hereditary 

 genes. For example, genes under any environmental 

 circumstances whatsoever never allow an egg with the 

 heritage of a worm to develop into a bird, nor do human 



