12 



C/iromoso^nes a?id Ectoplasm 



Jn a large measure our knowledge of the effects 

 of experimental means on cells Is the result of studies on 

 eggs. But in these studies the primary effect of the experi- 

 mental means on the protoplasmic system was often mis- 

 interpreted. Enthralled by the dramatic manoeuvres of 

 the chromosomes in mitosis investigators assumed for the 

 chromosomes an independence from the remainder of the 

 cell; this point of view easily led to the assumption that 

 external agents directly affect the chromosomes. So also, 

 the origin of mutations has been predicated upon inherent 

 activity of the chromosomes. 



The effects on marine eggs of changes in temperature, in 

 salinity or in hydrogen-ion concentration vary, depending 

 upon the eggs employed. For a species of eggs these effects 

 vary before and after insemination. For the fertilized egg 

 again there is a differential effect of the means which runs 

 with the mitotic cycle. But there is here no evidence to 

 indicate that this effect is primarily or only on the nucleus 

 or its chromosomes; what the experiments do show is that 

 the effect is first on the ectoplasm.^ 



These changes in the surrounding medium bring about 

 changes in the nucleus only secondarily. Always the ecto- 

 plasmic changes come first. Indeed, within optimum 

 range, the magnitude of the ectoplasmic changes determines 

 that of the nuclear. There is also a relationship between 

 the duration of the exposure of the egg to these changed 



1 Just, 1932. 



340 



