2 Charles Zeleny. 



W. The Rate of Differentiation during Regeneration of the Opercula in the SerpuHd, 



Apomatus yy 



V Regulation of the Rate of Growth and Nature of Differentiation during Regeneration 



of the Chelae of Gelasimus and Alpheus 8 1 



1 . Introduction 8 1 



2. Gelasimus pugilator 8 1 



3. Alpheus dentipes 85 



General Discussion 06 



General Introduction. 



That the development of an organ is dependent both quanti- 

 tatively and qualitatively not only upon the factors inherent in its 

 basis but also upon influences exerted by other parts of the body, 

 is a fact that has been especially emphasized by much of the recent 

 work in experimental embryology. The relative proportion of 

 the two influences varies in individual cases and its determination 

 has served as the objective point in various experimental studies. 

 The most valuable method in attacking these problems has un- 

 doubtedly been the one m which the regulation following mutila- 

 tion of the organism or change in its environment has been 

 observed. Assuming an interaction between the parts of an 

 organism, which is a necessary accompaniment of the idea of their 

 correlation, we must consider the animal or plant as a system 

 in equilibrium very nearly stable at certain periods, as in adults, 

 and with a unilateral instability at other periods, as in embryonic 

 development. This statement must apply not only to the organ- 

 ism as a whole but to all its parts and groups of parts individually. 



A disturbance of the normal relations of the parts, such as is 

 brought about by the removal of one of them or by the changing 

 of the external environment, must lead to changes which if the 

 system is not too rigid can give miportant light upon the normal 

 relations of the parts. This is the fundamental consideration 

 which lies at the base of all experimental biology and in the broad 

 sense of the term all such studies are studies in compensatory 

 regulation. 



Of special importance in the present consideration is the fact 

 that while the parts of an organism and their interactions are 

 continually undergoing change, especially during the period of 

 unilateral instability, the so-called embryonic period, these 

 changes are of a remarkably constant character for individuals 



