A CRITICAL EXAMINATION 37 



of somatogenesis to the problem of heredity. He 

 has been interested in other things. The second 

 is that in the main he has worked with material 

 of whose genetic history nothing was known. 

 His material was " unpedigreed " material. The 

 third is that embryology has generally studied only 

 one part, the beginning, of somatogenesis. Post- 

 embryonic development has been regarded as 

 unworthy of consideration. Yet in the main it is 

 with adult characters that the geneticist deals. 



These seem to be the more important practical 

 reasons why embryology has not hitherto been 

 conspicuously illuminating as a mode of genetic 

 research. Logically considered this method finds 

 its chief limitation, like each of the other three 

 methods, in that it takes hereditary specificities 

 as things given, and makes no attempt, because it 

 has no means of accomplishing such an end, to 

 investigate their origin or determination. 



From the methodological standpoint a sharp 

 distinction must, of course, be made between the 

 older purely descriptive embryology and the mod- 

 ern experimental embryology. It is the latter 

 which is of the greatest potential value as a mode 

 of research in genetics. The former (descriptive 

 embryology) is subject to a considerable degree 

 to the same practical limitation as cytology, 

 namely it is essentially a static method. It is 

 clear, however, that in experimental embryology, 

 using the term in the widest sense to include the 



