EXPERIMENTAL STUDIES ON THE DEVELOPMENT 



OF THE ORGANS IN THE EMBRYO OF 



THE FOWL (CALLUS DOMESTICUS). 



FRANK R. LTLL1E. 



I. INTRODUCTION. 



The results to be described under the above title relate to the 

 morphology, functions and power of regeneration of various 

 embryonic organs, and to the influence that certain embryonic 

 parts exert on the development of others. They represent the 

 application of a particular experimental method, viz., the destruc- 

 tion of definite parts, and study of the subsequent development. 

 Thus the particular organs studied are those most accessible to 

 operation, which form a rather heterogeneous assemblage. Nev- 

 ertheless, taken as a whole, the results form a contribution to 

 the subject of correlative differentiation of organs. 



The Principle of Correlative Differentiation in Embryology (i. e., 

 influence of the intraorganic environment in development) 1 is 

 that the rate, degree or mode of differentiation of any embryonic 

 rudiment is dependent on some part or parts of the same organism 

 (individual) external to itself; that is, that component parts of an 

 embryo determine mutually to a greater or lesser extent, their 

 respective lines and grades of differentiation. Much more is 

 meant by this than that any embryonic part can develop only in 

 its normal environment, which offers the prerequisites of its very 

 existence. The principle of correlative differentiation in fact im- 

 plies a distinction between a determinative and a non-determinative 

 environment, and the problem of correlative differentiation is so 

 far resolved when this is ascertained for all the organs (cf. Roux). 



Any part, the entire environment of which is non-determina- 

 tive, is said to develop by self -differentiation (Roux). 



These two principles do not stand in the relation of rival 

 theories but rather, probably, of cooperative factors in every 



1 Environment may be defined as conditions that influence dynamic processes in 

 protoplasm, and may be divided into extraorganic and intraorganic, the former being 

 external to the individual and the latter within its bounding surfaces. 



92 



