368 C, W. MITCHELL AND J. H. POWERS 



mother in the pedigree hne. This culture was treated according 

 to our regular method for inducing male production.^ The effect 

 was quite successful. Resting eggs followed. On January 20 

 sister eggs from one individual were isolated under conditions 

 favorable for hatching, which began by February 1. Ten of these 

 young were isolated in cultures normal as to food supply and to all 

 other known conditions. These ten individuals became the 

 parents of ten series which, for brevity, we designate collec- 

 tively as J 2. 



The effort was made to parallel J 2 with series derived from the 

 series U or /, but as already mentioned, difficulty is always expe- 



' In an article appearing in Science, vol. 38, pp. 786-788, A. Franklin ShuU, 

 in discussing this method of determining sex or male production, offers certain 

 objections based upon his study of Hydatina senta. In regard to the relation 

 of physiological rhythm, nutrition and male production, we should state that 

 since the last two may be directlj' controlled or modified by experimental 

 iconditions, and since the first may also be modified, though not by direct 

 methods, we have a means whereby we may govern this relation at will. 

 That Shull has healthy lines which pass through long periods of parthenogenetic 

 female production, is not surprising. We have had parallel cases; for instance, 

 one of our healthy lines had given rise to a continuous parthenogenetic female 

 production for over sixty generations. However, conditions were clearly not 

 such that male production was possible, but later when conditions were altered 

 to those favorable to male production, this hitherto total female-producing line 

 suddenly threw a large percentage of male producers. That this was due en- 

 tirely to some unknown internal factor would seem all but improbable. But 

 even accepting this, would it help in explaining results which have been obtained? 



In our study of sex determination we have attempted to emphasize that the 

 individual is the "point of action" rather than a number of generations. A 

 propos to this we would call attention to those cytological facts obtained by 

 Erlanger and Lauterborn (R. Zool. Anz., Bd. 20), Lensen (Zool. Anz., Bd. 21), 

 and Jennings (Bull. Mus. Comp. Zool., Harvard Coll., No. 30), upon Hydatina 

 and Asplancha which tend to prove that during the period of maturation sex is 

 determined by the casting off of the polar bodies. The reduction in the num- 

 ber of chromosomes occurring when the second polar body is cast off, results 

 in male production, while in ova which cast off only one polar body there 

 results female production. The time at which this maturation occurs cor- 

 responds to the time at which the factors we advocate are active in the deter- 

 mination of sex. It would be rather difficult to correlate this evidence, it geems 

 to us, with definite internal causes or to chemicals which act only upon the 

 preceding generation, as is offered in explanation of sex determination by 

 Shull. 



