6 MODES OF RESEARCH IN GENETICS 



greater or less degree to nearly if not quite all 

 living cells. The distinction between germ cells 

 and somatic cells in this regard is clearly one of 

 degree, not kind. 



Of much greater significance from the stand- 

 point of heredity than the potentiality for develop- 

 ment, though this of course in itself constitutes 

 one of the fundamental problems of biology, is 

 the specificity of the process, at once unique and 

 manifold. Not only does any particular hen's 

 egg produce always a hen, but it is also a par- 

 ticular kind of a hen which is produced, the par- 

 ticularity extending to the most minute details. 



So much then is, in general, to be objectively 

 observed about heredity ; namely, first the re- 

 semblance between genetically related adult in- 

 dividuals. Further, this resemblance is dependent 

 upon, because inseparably connected with, the 

 two processes of gametogenesis and somatogenesis. 1 



1 The discussion here and throughout has as primary material 

 objects of the reasoning sexually reproducing multicellular organ- 

 isms. Fundamentally it would appear, however, that there is no 

 essential difference, so far as the elements of the hereditary process 

 are concerned, between such higher forms, and the protozoa or other 

 forms reproducing asexually by fission or otherwise. Such a conclu- 

 sion seems certainly justified from Jennings' studies on inheritance 

 in Paramecium reproducing by fission. Cf. in particular, in this 

 connection, Jennings, "Heredity, Variation, and Evolution in Pro- 

 tozoa. I. The Fate of New Structural Characters in Paramecium, 

 in Connection with the Problem of the. Inheritance of Acquired 

 Characters in Unicellular Organisms." Jour. Exper. Zool., Vol. V, 

 pp. 577-632, 1908. 



