THE AMERICAN NATURALIST [ VOL. XLVH 



Making precise by means of our two rules this loose 

 and obscure proposition, it means the following experi- 

 mental situation. If two eggs side by side were identical 

 in cytoplasm and in environmental conditions (through- 

 out), but differed in their nuclei, the specified "heredi- 

 tary qualities" produced would differ. If the assertion 

 is that the nucleus is the exclusive "bearer," it further 

 means that if two eggs side by side were identical in nu- 

 cleus and in environmental conditions, but differed in 

 cytoplasm, the specified "hereditary qualities" pro- 

 duced would not differ. The questions are experimental 

 ones, of the highest interest, on which much work has 

 been done. 



But if the assertion is understood to mean that the 

 nucleus contains all the conditions necessary for the pro- 

 duction of the hereditary qualities; or if it means that 

 the characters produced are independent of the environ- 

 ment — of course experiments already tried show its in- 

 correctness. Only by reducing it to an experimental 

 situation does it become a profitable question. 



D. Some assert that the development of muscular 

 tissue or of nervous tissue (or the like) is determined 

 within the cells ; others dissent. 



This means that if the two cells were kept under same 

 conditions, one would still produce muscle, the other 

 nerve. It does not mean that the cell contains within 

 itself all the conditions necessary for the production of 

 muscle (or nerve) ; and it leaves open the question what 

 the two cells would produce if they were kept under di- 

 verse conditions. 



E. Some assert that the movement of a given organ- 

 ism is unequivocally determined by some external agent 

 (as light) ; others dissent. 



If the assertion is only that when two organisms are 

 alike in internal and in other external conditions, a dif- 

 ference in the light on the two may unequivocally deter- 

 mine a difference in movement, it is correct. If, on the 

 other hand, it asserts that when two organisms are sub- 



