90 THE SHORTER SCIENTIFIC PAPERS 



unicellular forms are smaller instead of larger. Some 

 investigations that I have undertaken indicate an answer 

 apparently meeting the conditions. While sufficient con- 

 trol experiments have not been made to venture more than 

 a provisional opinion, the data suggest that the cells of 

 cross-bred multicellular organisms are actually smaller 

 than the cells of inbred or pure line forms, and that the 

 more rapid division is a function of the greater ratio 

 surface has to volume in a small cell with the better op- 

 portunity thus obtained for increased metabolism. 



That there is need of further investigation on size and 

 variability in pure lines and in cross-bred forms through 

 the application of statistical methods in connection with 

 the maintenance of pedigrees through long series of gen- 

 erations seems evident. Eventually theories will make 

 way for facts which will allow a proper perspective. 



IV. 



Where do the results presented in the preceding pages 

 lead us? Does their value, so far as their bearing upon 

 the production of new and transmissible characters that 

 will build up an organism in a required direction, consist 

 merely in the formulating of hypothesis after hypothesis 

 which as investigations proceed will in turn make way for 

 other hypotheses equally transient? Or, on the other 

 hand, do they mark a definite progress along the lines we 

 are endeavoring to follow, namely, the control of evolu- 

 tion. 



Before attempting a reply which must prove more or 

 less unsatisfactory to those looking forward to immediate 

 results, it seems advisable to pause for a moment and in 

 the light of the preceding discussion consider the types of 

 differences — variations — which exist in so far as they may 

 effect the result with which we are chiefly concerned. 



Beginning at an early period in the history of evolution 

 with the idea that all variations might be inherited, re- 

 sults soon suggested that the characters due solely to 

 surrounding influences such as food supply, etc., were not 

 thus transmitted. These were called fluctuating varia- 



