DIFFERENTIATION, HEREDITY, SEX 297 



of association of which might differ in different species, as widely 

 as the groups of characteristics of the adults differ. 



The question as to just how the chromatic determiners (as- 

 suming their existence) really do affect the quality of the 

 reactions of the developing organism, is still practically un- 

 touched. To some it seems necessary to postulate the asym- 

 metrical distribution of the chromatin granules through suc- 

 cessive mitoses, so that certain kinds of granules or " deter- 

 miners" become distributed to certain cells and regions, directly 

 effecting there specific reactions. No such form of distribution 

 has been 1 observed, though indeed it has not been sought in a 

 thorough fashion. In tissues whose differentiation is fairly 

 advanced there are certainly characteristic and specific nuclear 

 appearances which indicate that the nuclei as well as the 

 cytoplasms have undergone a real differentiation, but whether 

 this is related to chromosome or granule structure remains 

 undemonstrated. 



If any such sorting out of determiners occurs it must be at 

 widely divergent stages of development in the various groups, 

 on account of the variety of the results in the way of specific 

 embryonic defect following the removal and pressure experi- 

 ments described above. Indeed the results of the pressure 

 experiments referred to, become highly significant from this 

 point of view, for it will be remembered that the presence of a 

 completely " foreign" nucleus may in some -cases not influence 

 the particular form of differentiation of the cytoplasm. To 

 say, in such cases as these and in the removal experiments, that 

 regeneration may occur and the proper determiners be reformed, 

 does not offer much that is helpful in the way of a solution of 

 this particular problem, for it would necessitate the assumption 

 of some mechanism back of the " determining " particles, by 

 which they themselves are formed and determined. 



The fact that parts, even small 1 bits, of a fully developed and 

 differentiated organism may finally, through a process of regu- 

 lation, give rise to a complete organism again, or that in many 

 plants, buds, bits of stem or leaf, may similarly give rise to a 

 completely formed organism capable of developing typical 



