74 



The Journal of Heredity 



However this may be, it does not, 

 of course detract at all from the vastly 

 greater significance to science of such 

 a conception as that which Child 

 presents. 



RELATION OF GENETICS 



From the standpoint of the geneticist 

 it is to be regretted that the author has 

 made no attempt to bring the facts of 

 genetics into relation with his theory. 



The geneticist, to some extent, is 

 able to deduce the nature of details 

 in cell organization from observed 

 differences among adults at the very 

 opposite end of the developmental 

 series. He finds an enormous number 

 of cases in which differences in adult 

 characteristics are inherited in such 

 a way as to make it necessary to 

 believe that they depend on differences 

 in real units of the cell organization. 

 These units can be handed on for an 

 indefinite number of generations, in 

 association with the most varied collec- 

 tions of other units, without suffering 

 change. If absent, they can not be 

 reconstituted by the cell. They must 

 divide as a rule with the most perfect 

 equality at each cell division. They 

 must, in short, be veritable organic 

 individuals, though merely of molecular 

 dimensions, living in the cell, and re- 

 producing by fission at each cell 

 division. 



Geneticists have not only learned 

 much about the nature of these entities 

 in the cell, but find a great deal of 

 evidence as to just where they live. 

 They are transmitted in inheritance as 

 if each were locatctl in a definite place 

 in one of a definite number of separate 

 chains. Evidence of the most direct 

 kind indicates that these chains, de- 

 duced from breeding ex|X'riments, are 

 none other than the chromosomes 

 actually visible in the cell nucleus. 



Geneticists, moreover, have dis- 

 covered the fact, rather embarrassing to 

 an extreme f)refonnation \iewpoin1, 

 that ihere is no relation between the 

 arrangement of these unils in the cell, 

 and the kind of characteristic of the 

 adult in which their absence or mcHli- 

 fication results in visible change. In 



the fruit fly for example, factors which 

 seem to affect only eye color are found 

 to be scattered at random among the 

 different chromosomes and the same 

 is true of factors which seem to affect 

 only eye shape, wing venation, body 

 color or bristles. In some cases more- 

 over, a single hereditary unit is respon- 

 sible for differences in apparently unre- 

 lated parts of the body. 



With all of this knowledge of the 

 ultra-microscopic constitution of the 

 cell, and of the one to one relations 

 between cell units and differences in 

 adult characteristics, the geneticist 

 can as yet say little as to how the unit 

 factors determine the course of develop- 

 ment. His scheme lacks motion. 

 Some such conception as that of 

 Child is needed to show how one 

 system gives rise to the other. Child's 

 theory on the other hand must take 

 account of the details of heredity if it 

 is to get beyond the vagueness which 

 leaves it rather obscure as to why one 

 egg develops into a cabbage, another 

 into a man with brown eyes and 

 another into a man with blue eyes. 



The location of unit factors in the 

 chromosomes, indeed their very exist- 

 ence, is, however, dismissed by the 

 author as an extreme and impossible 

 preformist view. He apparently looks 

 on the cell as an organization in a 

 particular kind of matter, determined 

 merely by a surface-interior gradient 

 in relation to external conditions. This 

 view overlooks the great body of 

 cytological evidence which indicates 

 that each of the chromosomes and, 

 indeed, each of the granules \isible 

 along the chromosoines in the thin 

 thread stage, is a self perpetuating 

 individual, as well as the genetic 

 evitlence for the indi\iduality of the 

 unit factors, referred to above. 



COMPATIUILITY OF SIMPLK MKCHANISMS 



OF ni;Ri:niTY, and dkvklof- 



mi<:nt wrrH a complkx 



CKLL or(;anization 



To the reviewer, however, the geneti- 

 cal and cytological conception of the 

 cell, as an association of independent 

 organisms, li\ing in .i rcl.it i\el\- large, 



