270 C. M. CHILD 



support the conclusion that inheritance is fundamentally the 

 same problem wherever a new living system arises from a part 

 of a preexisting system. 



The presentation of the following experiments on form regula- 

 tion as in part a study on heredity is then merelj^ the logical 

 consequence of a conception of heredity which I believe must 

 sooner or later find general adoption. 



The further objection may be made that in the development 

 of isolated pieces from adult organisms so many secondary fac- 

 tors connected with the morphological differentiation are involved 

 that the prospect of any real advance in our knowledge along 

 these lines is but slight. To such objections we may reply that 

 morphological differentiation exists in every egg cell, and more- 

 over, the fact that neither the egg in most cases, nor the sperma- 

 tozoon, is capable of initiating its own development when isolated, 

 indicates that before their union both these cells are, at least 

 often, more highly specified physiologically than, for example, 

 portions of a h^^drozoon or planarian body, in w^hich physical 

 or physiological isolation alone, without any stimulus comparable 

 to fertilization, is sufficient to initiate the development of a new 

 whole. The idea that the simplest, most primary conditions of 

 development exist in the gametes or the zygote is, I believe, 

 very far from being correct. The gamete before maturation is 

 very evidently a highly differentiated cell, it is physiologically 

 aged and in some cases in the last stages of senihty and approach- 

 ing death (Child, 'lib). Moreover, sexual reproduction is a 

 form of reproduction characteristic of relatively old organisms; 

 it is the last form of reproduction in the reproductive cycle. 

 To regard this as the most ' typical ' or the most important bio- 

 logically of the different forms of reproduction, and the one on 

 which alone we should base our theories or heredity, is to close 

 our eyes to a large part of the most significant facts of organic life. 



In the course of these studies I shall indicate what I consider 

 to be the bearing of the facts upon the general problem of 

 heredity, as well as their relation to the more special problems of 

 heredity which are associated with the particular form of repro- 

 duction involved. The work already accomplished during the 



