PRECIPITATION STRUCTURES SIMULATING ORGANIC GROWTH. 22 7 



function, consisting, as it typically does, in a definite and regular 

 succession of simpler processes, depends upon the presence of a 

 fixed and stable structural organization; without this there can 

 be no organization of processes, i. e., physiological organization, 

 any more than there can be organized or coordinated activity 

 without coordinated structure in an artificial mechanism like a 

 locomotive. In this sense structure is of primary importance in 

 any organism; the distinctive features of vital organization must 

 therefore be referred ultimately to special structural peculiarities. 

 This is obviously true of the various physical mechanisms and 

 devices subserving particular functions (like locomotion, vision, 

 circulation of blood, etc.) in higher animals; but it is the less 

 familiar application of this principle to the general conditions of 

 organic growth that I wish to consider in the present paper. 



The structural conditions present at a given time in a growing 

 or developing organism determine its present and future possi- 

 bilities of growth. In a certain sense this is already well recog- 

 nized ; a definite structure can be observed in many instances in 

 the germ before development, and certain features of this struc- 

 ture, especially the symmetry about certain axes and the dis- 

 tribution of certain materials, foreshadow the general morpho- 

 logical plan of the adult organism. 1 But in its details the struc- 

 ture of the egg is entirely different from that of the adult, and 

 its precise relation to the latter must be regarded as unknown; 

 i. e., we cannot say definitely why in any species the transfor- 

 mation of the germ and of the material which it incorporates 

 from the surroundings follows a constant and definite course, 

 leading to a definite final or adult stage. Since, however, the 

 building-up of organic structure from food and other materials 

 is obviously a matter of constructive metabolism, any physico- 

 chemical theory of development must assume that a main factor 

 in the formative process is the influence of the structural con- 

 ditions already present upon the metabolic transformations by 



1 For a general account of the known correspondences between the structure of 

 the egg and that of the adult, cf. Conklin's recent book, "Heredity and Environ- 

 ment in the Development of Man," Princeton University Press, 1918; also his recent 

 paper, "The Share of Egg and Sperm in Heredity," Proc. Nat. Acad. Sci., 1917, 

 Vol. 3, p. 101. 



