Studies on Regulation. JlJJ 



D. REGULATION AND EMBRYONIC DEVELOPMENT. 



The problem of regulation must be regarded as a part ot the 

 problem of development; indeed, as has already been abundantly 

 demonstrated the investigation of regulatory phenomena and 

 processes is ot fundamental importance as a means of throwing 

 light upon the problems of embryonic development. On the 

 other hand the phenomena of regulation and of ontogeny are in 

 certain respects so different that caution is always necessary in 

 extending conclusions from the one field to the other. 



Probably the most important field of investigation in connection 

 with regulatory phenomena is the determination by experimental 

 methods of the conditions and processes of morphogenesis. 

 Exact knowledge of these conditions and processes is of funda- 

 mental importance in biology, not only directly as an addition to 

 the data of science but indirectly as well, since it affords the only 

 means by which we can ever hope to attack intelligently certain 

 other problems, such for example as those of heredity and evolu- 

 tion. It is clearly impossible to obtain any intelligent conception 

 regarding the nature of the germ cells before we have determined 

 the relation between the adult organism and the cells from which 

 it arises. It is scarcely too much to say that the only satisfactory 

 method of determining what is inherited is the method of elimi- 

 nation: at any rate if we can determine experimentally what is 

 not inherited we shall be in a far better position to discuss the 

 nature of inheritance. Objection to these statements may be 

 made on the ground that it is possible to determine by direct 

 experiment, i. f., by hybridization or other forms of breeding, 

 that certain "characters," e. g., a color or a structural feature 

 are inherited in certain cases. Such an objection rests, however, 

 on a total misunderstanding of my position. The point I wish to 

 make is that the color or the structure is not itself inherited, 

 but only an unknown something that can give rise to the one 

 or the other under certain conditions. This is of course familiar 

 to all, yet it seems to be forgotten again and again. Qualities, 

 relations, and reactive capacities of protoplasm not "characters" 

 are inherited. Theories of heredity which regard the germ cell 

 as containing a multitude of elements, each representing some 

 character or group of characters in the developed organism are 

 the monstrous offspring of a morphology divorced from physiology 



