350 



THE AMERICAN NATURALIST 



[Vol. LIII 



There would seem to be no third possibility, as long as 

 we keep within the bounds of scientific explanation. But 

 a unit of structure may none the less be itself a chemical 

 individual. Modern speculative physics refers all quali- 

 tative differences in the last resort to differences of struc- 

 ture, even in the case of the elements. And it has been 

 suggested that the various specific protoplasms, Avhich 

 are responsible for the slightly different metabolic prod- 

 ucts of different species, owe their differences to stereo- 

 isomers, i. e., substances which agree quantitatively in 

 their composition, but whose enormously complex mole- 

 cules differ as the result of some slight transposition of 

 atoms or radicals.^! 



To the majority of present-day geneticists there is 

 doubtless a ready answer to the question: what is this 

 something that is common to all detached portions of an 

 organism which are capable of reconstructing the same 

 whole? It is likely that to most of them a completely 

 satisfactory answer would be: the cell nucleus. Thus 

 Jennings,^^^ in discussing specifically certain of the ques- 

 tions raised by Driesch, assures us that "the recent 

 study of genetics has shown that this [the chromosomal] 

 apparatus is the system on which the peculiarities of 

 development mainly depend. This system is not equi- 

 liotcntinl; ilic fate of its parts is not a function of their 

 ])i)sitioii: it has a complex structure with a correspond- 

 ino- comijlcxity of action; altering any of its parts alters 

 correspondingly the action of the system; irregular re- 

 moval or disarrangement of the parts destroys the 

 action." 



Whether or not this aggregate chromatin matter of the 

 nucleus constitutes the minimum dirisihle of the organ- 

 ism, as recent students of heredity are disposed to believe, 

 is still quite undc^cidcd. Kor j)rotozoa we are definitely 

 aMe to state thnt 111 - • i;\-))eriments in regen- 



