SEX-DETEEMINATION IN ASPLANCHNA 229 



physiological rhythm, high nutrition, and so forth, it was con- 

 ceived that a definite relation must also exist between the extremes 

 of this series as well, namely, between what we shall call the physi- 

 ological potential and amount of male production. Having 

 found that the type of rotifer, even regardless of ryhthm, could be 

 controlled through the factor of nutrition alone, it seemed that 

 this must be directly or indirectly a sex determining factor. The 

 experiments which follow were in large part directed towards as- 

 certaining the truth of these suppositions, that male production 

 and consequently sex-determination is a matter of physiological 

 potential and under the more or less direct control of nutrition. 

 It was hoped that the degree of such relation might be rendered 

 fairly definite. Search* was also made, however, for any other 

 factors, major or minor, negative or positive, which may play 

 a role in sex-determination. 



Throughout all experiments the same technique was used in 

 rearing the Asplanchna as was described in a preceding article,^ 

 consequently details need not be. given here. The food supply 

 consisted of a mixed diet of Paramecia, Hydatina, and Brachi- 

 onus by which the humped type as well as the saccate type could 

 be continually reared. 



MASS CULTURE FROM SACCATES 



During the winter of 1910-1911, a number of pedigree series 

 were reared which remained in the saccate form throughout many 

 generations and showed but few instances of male production. 

 As offshoots from these series thirteen mass cultures were started, 

 from time to time, to determine the influence of such conditions 

 upon the form, type, as well as male production. The histories 

 of these mass cultures are given in table 1.^ Examination of 

 the table will show that in seven of these cultures the transition 

 to the humped type occurred and that in four of this same num- 

 ber males were also formed. 



* C. W. Mitchell: Jour. Exp. ZooL, vol. 15, pp. 91-130. 

 ^ Table 2 of preceding paper. 



