SEX-DETERMINATION IN ASPLANCHNA 233 



HIGH NUTRITION FOLLOWED BY BRIEF STARVATION 



Fifteen new mass cultures were started from the general stock 

 as above, some of them begun from humped mdividuals while 

 others were started from saccates which were then so fed as im- 

 mediately to bring about the transition. All the cultures were 

 full-fed and the following three-fold test showed in general the 

 success of the feeding: first, the humped type as soon as pro- 

 duced was maintained; second, the digestive tracts of all indi- 

 viduals examined contained abundance of food; while, third, un- 

 captured food remained free in the cultures, A soon as these 

 nutritional conditions were established each culture was starved 

 at least once for a period of twenty-four hours. The results 

 from two of these cultures, four and nine, may best be ignored 

 for they had produced males before starvation. Nothing in their 

 conduct contradicts the results of the other cultures in the exper- 

 iment although the results with them were more complex. A 

 detailed description of the results is given in table 2. 



In eight of the remaining thirteen cultures copious male pro- 

 duction followed closely (within twenty-four hours or less) upon 

 the starvation period, while five cultures produced no males, one 

 of them reverting to the saccate form as a result of the starva- 

 tion. One culture (11) was subjected to repeated periods of 

 starvation; no second production of males followed, but instead 

 a retrogression to the saccate type. 



This immediate male production, following in eight out of fif- 

 teen cases of combined high feeding and starvation, is at once 

 suggestive as confirmation of our previous hypothesis as to the 

 cause of male production. Moreover, it is easily possible to in- 

 terpret the five cases of failure. They were all cultures in which 

 the transition from saccate to humped form had but recently 

 taken place; this was also true in a portion of the eight positive 

 cultures. But, it is natural to assume that the food stimulus 

 which had brought about the transition by so raising the physio- 

 logical level in the different cultures that the humped type was 

 produced, had not acted long enough or with sufficient force to 

 make male production possible in the five, while it had in the 



