SEX-DETERMINATION IN ASPLANCHNA 239 



Individual young from each of twenty cultures were again iso- 

 lated in like cultures and allowed to reproduce. These were also 

 parthenogenetic females. A third generation was reared in nine 

 of the latter cultures under the same conditions with a corre- 

 sponding result of no male production. The more detailed his- 

 tory is given in table 5. As expected from previous experiments, 

 both with mass and individual cultures, there was accompanying 

 this non-male production a reversion to the saccate type which 

 was all but universal. 



This experiment was made with a double purpose, that of 

 checking our results with those obtained from the mass culture 

 experiments as well as checking the starvation experiments of 

 Punnett, Whitney, and Shull on the rotifer H. senta. Our re- 

 sults agree fully with those of the two former experimenters but 

 are somewhat at varience with those of the latter. We shall 

 return to this apparent disagreement in the final discussion. 



STARVATION OF INDIVIDUALS CHOSEN FROM LINES AT PERIODS 

 OF HIGH POTENTIAL 



In order to experiment with material of high potential and 

 homogenous character, forty individuals were derived from four 

 parents. Two of these parents were chosen from Series E and two 

 from Series D, both series being at the time in question in the full 

 humped type and in a crescendo of reproduction. Of the four 

 individuals, two from each series were isolated in cultures of low 

 nutrition while tRe other two corresponding individuals were iso- 

 lated in cultures of high nutrition. These four individuals thus 

 situated produced the forty young above mentioned; each of 

 these was isolated at birth. Of these young thus isolated one 

 or more from each parent were used as controls and placed under 

 nutritive conditions identical to those of the well-fed parents. 

 All the others, when isolated shortly after birth, were subjected 

 to eight to ten hours complete starvation, followed by uniform 

 and abundant food. The detailed results are given in table 6. 



The results confirm in high degree previous expectations. In- 

 dividuals from poorly nourished parents themselves subjected to 

 starvation followed by high feeding gave no male producers. In- 



