82 NATIONAL TRENDS IN BIOLOGY 



the rate and intensity of metabolism causes the structural 

 and chemical correlation of the rest of the body. From 

 these deductions, in turn, two further points should be 

 noted: (1) that as each part of the lower animals, as well 

 as the early (embryonic) cells and tissues of higher ani- 

 mals, have the potentiality of becoming what any other 

 cell or tissue does become, the growth action of such 

 parts is always positive; while (2) the head region in its 

 exercise of an inhibitory, coordinative, and regulative 

 action is negative. In criticism of the theory, one may 

 quote G. H. Parker, of Harvard University, who, in lead- 

 ing the discussion of the subject in 1924, at Toronto, 

 called attention to the fact that even before Child had 

 brought forth his evidence for the Axial Gradient Theory, 

 most biological workers had already observed enough 

 similar results from their embryological work to agree 

 with Child on his statements of fact, but that the theory 

 has given no further information than was already known 

 about why anything does what it does. 



The Metabolic Theory of Sex. Another metabolic the- 

 ory of note is that commonly called the Goldschmidt 

 Theory (1923). At the moment there is a dispute between 

 the followers of Riddle and Goldschmidt as to who has the 

 prior claim for its promulgation. All biological workers 

 are familiar with Morgan's work demonstrating that the 

 so-called sex chromosomes are the determiners of sex. 

 Morgan's explanation is a qualitative one. Goldschmidt 

 has devised a quantitative theory, sometimes called the 



