ACTIVATION OF STARFISH EGGS BY BUTYRIC ACID. I 



developmental sequence may appear, its initiation is almost 

 certainly dependent upon some slight and non-specific and 

 primarily structural alteration in the egg-system. 



In the orderly progress of development from one stage to the 

 next we must similarly assume at every stage a similar inter- 

 dependence between the existing structural conditions and the 

 rate and character of the form-determining as well as other metab- 

 olism. Each step in advance is thus largely a consequence of 

 the immediately preceding structural modification, and in its 

 own turn furnishes the structural conditions determining the 

 next step. From this point of view the unification of the whole 

 developmental sequence would seem to be conditioned, at least 

 in its main features, by specific structural peculiarities, repre- 

 sented at the beginning of development by the inherited organ- 

 ization of the germ. This determines at the start assuming 

 normal external conditions the course of the ensuing trans- 

 formations, and hence the special kind of structure arising at 

 each successive stage of development. Structure, however, is 

 not alone to be considered; the germ is a metabolizing system, 

 and the soluble and diffusible (non-structural) materials formed 

 in metabolism undoubtedly also play an essential part, probably 

 chiefly of a controlling or regulative kind (e. g., as hormones). 

 And since throughout development there is always this reciprocal 

 interdependence between structure and metabolism, it is clear 

 that such materials which presumably change continually in 

 their character as development proceeds must influence at 

 every stage the nature of the metabolic transformations and 

 hence of the organized structure which is being built up. It 

 seems further probable that the destruction or removal of in- 

 hibiting or injurious or anticatalytic compounds, as well as the 

 formation and activation of specific catalysts (enzymes), is con- 

 cerned in the developmental process from the very first. 1 In 

 brief, the metabolism of the developing germ must be regarded 

 as differing not qualitatively but only in certain of its quantitative 

 aspects especially in the predominance of growth and formative 

 processes from that of the adult organism. 



1 This is indicated (e.g.) by the existence in the sea-urchin egg of an antibody for 

 the sperm-agglutinin or "fertilizin" (F. R. Lillie, Journal of Experimental Zoology, 

 1914, Vol. 16, p. 544). 



