SEX-DETERMINATION IN ASPLANCHNA 231 



lines, and second, the conclusion, previously mentioned, that 

 male production is partially though not completely correlated 

 with the appearance of the humped type. In none of the six 

 saccate culture^ were males produced. 



In the spring of 1911 a definite method was discovered by 

 which the humped type might be produced and reared at will. 

 Besides isolation cultures, sixteen mass cultures of this type were 

 started. By means of these cultures such experiments as our 

 facilities allowed were made to test the influence of temperature 

 change. Although the experiments, owing to limited facilities, 

 were not performed with the precision desired, yet the results of 

 ample observation agree fully with the results of Shull, Nussbaum, 

 and Punnett. Temperature, within fairly wide limits, is essen- 

 tially a negative factor in regard to sex-determination, 



LOW FEEDING AND STARVATION 



Fifty mass cultures of the humped type, drawn from the same 

 pedigree series as the preceding, were treated as follows: The 

 ordinary culture medium was filtered and to the filtrate a mini- 

 mum quantity of food was added. This formed the fluid medium 

 of each culture and compelled low feeding, to practical starva- 

 tion, of the individuals. The chief results were similar to those 

 described in the previous paper, namely, degenerative changes 

 resulting in transitional individuals, then the saccate type. In 

 only two out of the fifty cultures were males produced during 

 the two to three weeks which they were maintained. The results 

 thus, of general starvation in mass cultures, resemble those of 

 some of Nussbaum' s experiments on Hydatina senta, which like- 

 wise resulted in parthenogenetic female production. An added 

 interest attaches to the results of starvation on A. amphora, in 

 that the regressive change from the larger humped type to the 

 smaller saccate type, discloses the tendency toward the lowered 

 physiological potential already mentioned in connection with 

 this form. 



