NUCLEOPLASMIC RELATIONS IN ARCELLA 93 



branches" (p. 520). The length of the spines of Arcella dentata 

 did not seem to the writer to be a favorable character for selec- 

 tion work and hence was neglected in favor of spine number and 

 diameter of the shell. Great variations in length of spine were 

 frequently encountered, but they were so obviously due to the 

 effects of environmental factors that it was not considered ad- 

 visable to undertake a study of them from the selection stand- 

 point. As we have seen, there appear to be among the groups 

 of Arcella polypora at least two characters that vary independ- 

 ently, i.e., the diameter of the shell and the diameter of the 

 mouth of the shell. Selection work with these characters would 

 probably prove them to be independent and would thus furnish 

 a case similar to that noted by Jennings in Difflugia. 



How can we interpret these independently varying characters 

 in the light of our investigations on Arcella? Nothing, of course, 

 can be stated with certainty, but it may be worth while to make 

 suggestions. If the assumption is correct that the daughter nu- 

 clei formed during vegetative reproduction are qualitatively dif- 

 ferent, then there is no reason why all of the characters of the 

 organism should be correlated. Adopting the current theory 

 that the determiners for different characters are represented in 

 the nuclear chromatin by different molecules or group of mole- 

 cules, there seems to be no reason why in these organisms ine- 

 qualities may not occur independently in the different determiners 

 resulting in corresponding inequalities in the different external 

 characters. If the external characters are all correlated, we may 

 assume that their determiners are linked in some way that leads 

 to similar interdependent variations. 



It is, of course, possible that independent characters are rep- 

 resented within the chromatin by multiple factors and that the 

 inequality hypothecated consists not in an unequal division of 

 one determiner but in the unequal distribution of a number o^ 

 determiners to the daughter nuclei. 



The cutting experiments on Arcella dentata lessen the possi- 

 bility that the cytoplasm plays an important role in the produc- 

 tion of the heritable diversities observed. The chromidia as a 

 factor in this process seem also to be ruled out by these experi- 



