28o PATTERNS AND PROBLEMS OF DEVELOPMENT 



is of fundamental importance. The following discussion of this question 

 is quoted from a recent paper. 



Some biologists apparently believe that metabolism is not a fundamental factor 

 in development. For example, Shearer [1930, p. 266] says: "morphological organiza- 

 tion has nothing to do with metabolism." Parker [1929, p. 424], in criticizing the 

 gradient concept, makes the statement: "the metabolic activity of the organism is not 

 a true formative process, but the result of such a process." Spemann [1939, pp. 321 ff.] 

 seems to hold somewhat the same opinion; his discussion of gradients involves the mis- 

 taken assumption that, according to the gradient theory, there must be only quantita- 

 tive metabolic differences in the amphibian egg at the beginning of embryonic develop- 

 ment. In his recent book, Weiss [1939, pp. 373-83] seems to hold that specifically 

 different capacities for organization exist in different regions independently of metabo- 

 lism. Granting that these capacities are present in many eggs, how did they arise 

 except through metabolism? And even if they are present in eggs, are they present in 

 the early stages of buds, of pieces of Tubularia or Corymorpha stem or in aggregates of 

 dissociated Corymorpha cells? In isolated pieces of the planarian body, of various 

 annelids and of some ascidians development of a particular part has no definite or 

 constant relation to a particular region of the individual or to a pre-existing organiza- 

 tion, but a new organization originates. Does it originate independently of metabo- 

 lism? If we inhibit metabolism it does not appear and in many cases it is possible to 

 initiate its development by purely quantitative external differentials which in one way 

 or another determine gradients involving metabolism. It has been pointed out re- 

 peatedly that, even if these gradients are primarily quantitative, they probably do not 

 remain so for any great length of time, though quantitative factors may continue to 

 exist and be effective, even in many adult animals. How do the regional organizing 

 capacities and the presumably specifically different metabolisms of hydranth, stem 

 and holdfast region in a reconstituting piece of Corymorpha originate if not through 

 metabolism? Since any level of a new individual may develop from any level of the 



stem these capacities are certainly not localized preceding isolation of a piece 



The arguments of Spemann and Weiss are based on the egg and embryonic develop- 

 ment rather than on development in general Like many other embryologists 



they maintain that organization or specific capacity for it is present, but do not tell us 

 how it originates. If organization consists in localized presence of specific substances 

 how can these substances originate and be localized except in the final analysis through 

 metabolism? Probably no one now believes that they are aU present in the primitive 

 germ cell. It is difiicult to believe, for example, that localized formation of specific 

 substances in the dorsal inductor region of the amphibian egg and embryo can take 

 place independently of metabolism. Without metabolism ovarian development of the 

 oocyte and embryonic development cease. Even the differentiation of various organs 

 and tissues does not persist if their metabohsm is decreased below certain levels. How 

 are electric and other physiological regional differences established and maintained 

 except through metabolism? What is the possible nature of formative processes as- 

 sumed to be independent of metabolism? In short, is there any more fundamental 

 characteristic of hving protoplasms than metabolism? At present evidence of any such 

 characteristic seems to be whoU}- lacking. It may be argued that structure of some 

 sort is more fundamental, but structure without metabolism is not living protoplasm 



