ISO C. M. CHILD. 



us when we attempt to apply it to the phenomena of form-regu- 

 lation. Some of the special cases discussed by Morgan will be 

 considered more fully elsewhere in connection with new experi- 

 mental data. 



Such a hypothesis appears to me a totally unnecessary as- 

 sumption in most cases, probably in all. Moreover, it does not 

 afford a satisfactory explanation of the facts. I have recently made 

 an attempt to account for some of the facts of regulation in a some- 

 what different manner, 1 and without assuming the existence of a 

 series of substances which seem to me to make comprehension 

 more difficult. 



THE NATURE OF FORMATIVE PROCESSES. 



The chief peculiarity, and, as I believe, the fundamental error 

 in the hypotheses of formative substances seems to be that they 

 regard the process of morphogenesis as something sni generis 

 and not as simply a part of the dynamic or functional activity of 

 the organism. The activities of the organism are considered as 

 two-fold, one group being concerned with the construction of a 

 complex machine, the other with the functions of that machine 

 when completed. According to this view development is pri- 

 marily a period of construction and not of function. This idea is 

 perhaps a natural consequence of the separation of morphology 

 from physiology. But when we consider the data already at 

 hand it seems impossible to make any such distinction. The 

 organism is primarily and at all times a dynamic or functional 

 complex and the process of morphogenesis is merely an incident, 

 or, in other words, structure is a visible by-product of these 

 activities. In short, it is rather the result of the relations of parts 

 than of any " formative" capacity existing in the single elements 

 themselves, and as regards any given element or unit of the organ- 

 ism the factors of the environment and not the element itself must 

 be, as we have seen, in the final analysis, the real formative factors. 

 These environmental factors may be otherwise designated as the 

 functional or dynamic conditions and we may regard development 

 as primarily a functional process. 



1 Koux' 1 s Arc/iir., XX., 3, 1906. 



