450 THE AMERICAN NATURALIST [Vol. XLIV 



acters of the individual. One school looks npon the egg 

 and sperm as containing samples or particles of all the 

 characters of the species, race, line, or even of the indi- 

 vidual. This view I shall speak of as the particulate 

 Hi voril of development. 



The other school interprets the egg or sperm as a kind 

 of material capable of progressing in definite ways as it 

 passes through a series of stages that we call its develop- 

 ment. I shall rail this view the theory of pliysico-chem<- 

 ical reaction, or briefly the reaction theory. The resem- 

 blance of this comparison to the traditional theories of 

 preformation and epigenesis is obvious, and I should 

 willingly make the substitution of terms were it not that 

 the terms preformation and epigenesis have certain his- 

 torical implications, and, as I wish to emphasize certain 

 things not necessarily implied in the historical usage, I 

 prefer descriptive terms other than these overladen with 

 so many traditions. 



A few preliminary considerations will serve to clear 

 the way for the detailed examination to follow : 



The particulate theory may appear more tangible, 

 definite and concrete because it seems to make a more 

 direct appeal to a material basis of development and 

 heredity. The theory of physico-chemical reaction may 

 seem more vague and elusive, since the responses and 

 reactions to which it must appeal are as yet little known. 

 But this distinction is not one of much importance. For 

 the particulate theory requires as elaborate a series of 

 processes or changes to account for the distribution of 

 the postulated particles and their development into char- 

 acters as does the reaction theory itself, and on the 

 other hand the reaction theory may rest its claims on 

 as definite a physical or material basis as does the 

 other view. One theory lays emphasis on the material 

 particles of development, the other on the changes or ac- 

 tivities in the same material. Both views assume that 

 there is something in the egg that is responsible for 

 every detail of character that later develops out of the 

 egg. Since we do not know what this something is, it 



