32 C. M. CHILD. 



and value of recent work on breeding and hybridization, but is 

 merely to state its limitations. The sexual breeding of higher 

 animals does not and cannot at present, if ever, go much beyond 

 the determination of empirical symbolic formulae. We can say 

 that the combination of x and y gives 2, but all are unknown quan- 

 tities and breeding experiments of this character cannot make 

 them anything else. They do not solve the problem but merely 

 state it in symbolic terms. 



To understand, or even to foimulate the processes of inherit- 

 ance we must first of all know the processes in the individual 

 and we must investigate the process of reproduction in its 

 simplest forms. When we have done this we shall be better 

 able to attack the problems involved in the more complex proc- 

 esses of sexual reproduction. 



We have, I believe, in the experimental reproductions, i. e., in 

 the regulation of isolated pieces, a field of the greatest importance 

 for the investigation of inheritance. Here we can vary the size 

 of the reproductive element, the region of the body from which 

 it comes, the conditions under which it shall regulate and the 

 conditions under which the parent organism lives before the piece 

 is isolated. And I have already shown in part (Child, 'nc, 'lid) 

 and shall show further in later papers that all these factors are of 

 importance in inheritance. Moreover the organism is primarily 

 a dynamic system, a complex of processes, it is comparable rather 

 to a river with its current of energy and its morphological limiting 

 conditions (Child, 'lie) than to a machine in the ordinary sense. 

 Sooner or later we must interpret the organism in terms of 

 dynamics rather than in terms of morphological entities. Many 

 years ago Huxley said of the cells: "They are no more the pro- 

 ducers of the vital phenomena than the shells scattered along 

 the sea-beach are the instruments by which the gravitative force 

 of the moon acts upon the ocean. Like these, the cells mark 

 only where the vital tides have been, and how they have acted." 

 These words, written more than a generation ago, have lost none 

 of their value and may well serve to-day as a guide to biological 

 investigation and a warning against certain types of biological 

 theory. 



Let us take the case of the chromosome, for example, which 



