254 ROLE OF CYTOPLASM [CH. 



differ from Echinoid eggs, not in the fact that in one the 

 parts are definitely determined while in the other they are 

 more or less indeterminate, but that in the one determina- 

 tion appears early and in the other later. At some stage 

 in every egg, so far as is known, the parts are equipotential, 

 and from such a homogeneous egg heterogeneity arises 

 sooner or later. Fundamentally, it is on this production 

 of heterogeneity from the homogeneous apart from external 

 influence that DRIESCH bases his belief in the inadequacy of 

 physico-chemical forces to explain development. 



The general conclusion to be reached with regard to the 

 function of the cytoplasm in development and inheritance 

 is that it cannot be relegated to the position of a mere 

 medium in which the chromosomes carry on their activities, 

 but that it plays an essential part in the process. By the 

 nature of the case it is not possible to ascribe to it definite 

 functions in the same way that it may be assumed, with 

 something like probability, that the chromosomes are re- 

 sponsible for the segregation of Mendelian characters in 

 inheritance. The chromosomes are definite entities, possibly 

 even probably retaining their individuality from one cell 

 generation to the next, while the cytoplasm is a complex in 

 which, at present, it has not been possible as a rule to observe 

 the different parts separately and continuously. But the 

 chromosomes and cytoplasm together are parts of a con- 

 tinuous whole; it is no more possible to regard the chromo- 

 somes as acting independently than to think of the brain 

 functioning apart from the body, and perhaps the crude 

 chemical analogy of the parallel series CH 3 H, CH 3 C1, 

 CH 3 OH and C 2 H 5 H, C 2 H 5 C1, C 2 H 5 OH, given in the pre- 

 ceding chapter, expresses the idea of the relation as well as 

 any single metaphor that can be devised. But this analogy 

 fails in one important respect, for it can hardly be doubted 



