442 The American Naturalist. [June, 



gather into one sketch an outline of the view of the process of 

 development which these different publications have hinged 

 upon. 



The problems involved in a theory of organic development 

 may be gathered up under three great heads : Ontogeny, Phy- 

 togeny, Heredity. The general consideration, the " factor " 

 which I propose to bring out, is operative in the first instance, 

 in the field of Ontogeny ; I shall consequently speak first of the 

 problem of Ontogeny, then of that of Phytogeny, in so far as 

 the topic dealt with makes it necessary, then of that of Her- 

 edity, under the same limitation, and finally, give some defi- 

 nitions and conclusions. 



Ontogeny : " Organic Selection " (see ref. 2, chap, vii).— The 

 series of facts which investigation in this field has to deal with 

 are those of the individual creature's development ; and two 

 sorts of facts may be distinguished from the point of view of 

 the functions which an organism performs in the course of his life 

 history. There is, in the first place, the development of his 

 heredity impulse, the unfolding of his heredity in the forms 

 and functions which characterize his kind, together with the 

 congenital variations which characterize the particular indi- 

 ual— the phylogenetic variations, which are constitutional to 

 him ; and there is, in the second place, the series of functions, 

 acts, etc., which he learns to do himself in the course of his life. 

 All of these latter, the special modifications ivhich an organism 

 undergoes during its ontogeny, thrown together, have been called 

 "acquired characters," and we may use that expression or 

 adopt one recently suggested by Osborn, 2 " ontogenic varia- 

 tions " (except that I should prefer the form " ontogenetic 

 variations "), if the word variations seems appropriate at all. 



2 Reported in Science, April 3rd. ; also used by him before N. Y. Acad, of Sci., 

 April 13th. There is some confusion between the two terminations « genie " and 

 "genetic." I think the proper distinction is that which reserves the former, 

 "genie," for application in cases in which the word to which it is affixed qualifies 

 the other, "genetic" conveys similarly a passive sig- 

 nification ; thus agencies, causes, influences, etc., and "ontogenic phylogenic, 

 rod " ontogenetic, phylogenetic, etc." 



