268 C. M. CHILD 



asexual, giving rise to a whole or to a part, enters upon the develop- 

 mental process. And the process of inheritance is the process 

 of origin and development of these capacities in the reproductive 

 element. In short, heredity is what the reproductive element 

 brings with it from its past. If the sex cells, like the asexual 

 reproductive elements and the artificial elements resulting from 

 the isolation of pieces by operation, are at some earlier stage of 

 their development physiologically parts of the organism, and 

 there are very strong reasons for believing that they are, then we 

 may define heredity as the capacity of a physiologically or physi- 

 cally isolated part for regulation. 



The only way in which we can discover anything concerning 

 this capacity is by allowing the regulation to occur under the 

 most various and carefully controlled conditions, i. e., we can 

 investigate and analyze the problem of heredity only with the 

 aid of development. At some time in the future it may be pos- 

 sible to determine directly by physical and chemical analysis 

 of the reproductive element what its capacities for development 

 are, but at present we know so little concerning the relation 

 between constitution and capacity that for the most part we can 

 recognize capacities only as they are realized in the course of 

 development. 



Heredity is involved not only in the development of new wholes 

 from reproductive elements but in the reproduction of parts. 

 Every cell division is as truly a special problem in heredity as is 

 any other reproduction. The reappearance of the same number 

 of chromosomes in successive generations of cells is as truly a 

 case of heredity as is the reappearance of five fingers on the hand 

 in successive generations of man. Montgomery has said that 

 we understand heredity so far as we know the behavior of chromo- 

 somes (Montgomery, '06, p. 56). It seems to me that it would 

 be much more nearly correct to invert this statement and say 

 that we understand the behavior of chromosomes so far as we 

 understand heredity. 



As soon as we view the problem of heredity from this broad 

 general standpoint it becomes clear that wherever in the organic 

 world reproduction occurs, there is heredity also. Moreover, 



