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THE AMERICAN NATURALIST [Vol.LVI 



clear, in the light of modern genetics, embryology and 

 cytology, that what actually happens is a reduplication 

 generation after generation of germinal protoplasm. 

 That is, the proteins already present in the germ-cell not 

 only determine what will be built up in growth, but also 

 the composition of that overgrowth which, as a detached 

 individual, constitutes the physical basis of inheritance. 

 If the initial protoplasmic substance is chemically specific 

 then inevitably the anatomical and physiological com- 

 plexities which arise out of it must likewise be specific. 



Before we can grapple with the problem of the possible 

 induction of changes in this fundamental mechanism 

 through influences emanating from the body, we must 

 consider some matters concerned with embryonic develop- 

 ment and the fundamental chemical nature of the somatic 

 cells. 



As to how the constitution of the egg becomes trans- 

 formed into that of the adult, the most consistent and 

 reasonable hypothesis to date, in my opinion, is that 

 proposed by Child, based on axial or metabolic gradients. 

 A full exposition of his hypothesis must be sought in his 

 books, " Individuality in Organisms " and " The Origin 

 and Development of the Nervous System from a Physio- 

 logical. Viewpoint." I can sketch only such aspects of it 

 as pertain to my present subject. Starting with tlie 

 universally accepted biological axiom thai excitability 

 followed by some degree of transmissibilii \ i< a t'lmda- 

 mental property of all living matter, Cliild believes, as I 

 understand him, that the establishment of i)ohirity in the 

 fundamental organismic proteins of the germ-cell is the 

 beginning of development. The eggs of many species al- 

 ready show polarity (animal and vegetal pole) at the time 

 of ovulation; in other forms polarity i> not established 

 until later. In the former case [lie polaritx- may liave 

 been determined in earlier cell-generations by extrinsic 

 factors or it may be due to the original position of the 

 o\aim in the ovary with reference to the nutritive stream. 

 Yolk ai)])arently accunmlates in the region of least oxida- 

 tion and thus ijiarks the vegetal i)ole. In the second type 

 of eu- polarity, at lii'st laekin- is <nou established 

 because <li tTereiitial environmental exi^oMire (ditreivnce 

 in oxygen supply, light, contact, general surface exposure, 



