314 



A. FRANKLIN SHULL 



was able to demonstrate changes of relative nuclear volume 

 related to the seasons and certain environmental factors (tem- 

 perature, chemical substances). One misses in his paper, how- 

 ever, the accurate relation of these changes to the life-cycle. It 



TABLE 9 

 Relative size of nuclei in three tissues of male-producing and female-producing 

 rotifers of the same origin, reared under the same conditions 



is not clear what changes in the mode of reproduction accom- 

 panied the nuclear changes. One is left to infer, on the basis of 

 work by earlier authors, that changes in temperature and of the 

 chemistry of the water bring on the changes of reproduction. 

 The weakness of such argument is mainly that the nuclear changes 

 might be incidental, might be other effects of the same cause, and 



