250 CLAUDE W. MITCHELL 



tion to no male production is also interpretable as due to a low- 

 ering of vitality, resulting, possibly, from too uniform feeding. 



In Whitney's first work^ on Hydatina, we find marked advance 

 in the definite proof that the 'strains' of Punnett may be de- 

 rived from one and the same pure race and may freely give rise 

 to each other. Definite external causes, however, were not as- 

 signed for the transitions. Starvation experiments were tried with- 

 out apparently modifying male production. But it must again 

 be pointed out that Whitney did not consider the nutritive con- 

 dition either of the race or of the individual from which the 

 starved animals were derived. 



In later articles Whitney develops first the rather theoretical 

 hypothesis of some chemical substance dissolved in the culture 

 medium as the cause of male production, while in a later pub- 

 lication^ he demonstrates the negative influence of certain cul- 

 ture media as inhibitory of male production, agreeing thus essen- 

 tially with Shull. We return to this matter later. But for the 

 present and from our stand point the conduct of Whitney's chief 

 series as recorded in his second article^ is of special interest. 

 Two series were reared for one hundred generations fed upon a 

 uniform diet of the flagellate, Polytoma, for which was 'then 

 substituted the flagellate, Chlamydomonas. Throughout the en- 

 tire one hundred generations fed upon the uniform diet no males 

 appeared. But immediately — within a few generations after the 

 food change — copious male production occurred. Still Whitney 

 does not see in this striking sequence even the probability that 

 change in nutrition induces male production. He evidently re- 

 gards the influence of nutrition as a discarded hypothesis although 

 in his latest work as well, several instances occur where results 

 strongly suggest the influence of this factor. It is worth noting 

 that in our cultures of A. amphora, preceding the work for the 

 present paper, there occurred an instance practically duplicating 

 Whitney's experiment. A pedigree series uniformly fed upon 

 Paramecia for fifty-seven generations had shown not a single 

 male producer. Then upon sudden substitution of Euglena for 



« Jour. Exp. Zool., vol. 5, p. 1-26, 1907-1908. 



7 Jour. Exp. Zool., vol. 12, no. 3, pp. 227-62. 



8 Science, N. S., vol. 32, pp. 345-49. 



