NUCLEAE VOLUME AND LIFE-CYCLE OF HYDATINA 295 



less be greater in one kind of female than the other. An investi- 

 gation of the nuclear volume offered a test of this suggestion. 



TESTS EMPLOYED 



Periodicity of male-production. One of the lines of rotifers used 

 for this study showed to a marked degree the periodicity of male- 

 production which I have described (Shull, '15) as being common 

 in other lines. This line was reared in a way which would show 

 the periodicity more sharply than the usual complete family- 

 pedigree method. A dozen young female-producing females of 

 about the same age were placed together in a dish, where they 

 were kept until about twenty-four hours after egg-laying began. 

 They were then removed to another dish and given fresh food. 

 The young hatching from the first eggs laid after this transfer 

 were isolated and reared to maturity, the number of male-pro- 

 ducers and female-producers being recorded. From the female- 

 producers a number were selected and, about twenty-four hours 

 after their egg-laying began, put into a dish with fresh food. 

 The earliest-hatching young in this dish, up to as high a number 

 as could conveniently be handled, were isolated as before and 

 reared to maturity, the number of male-producers and female- 

 producers being again recorded. By this means a series of 

 generations was obtained in which the confusion arising from the 

 overlapping of late members of one generation and the early 

 members of the next is avoided. The famihes are not complete, 

 each generation being represented only by members from the 

 middle of the family, at which time they are most likely (Shull, 

 '10) to be male-producers. 



The periodicity of male-production in this line is quite evident 

 from the records which are given in table 1. Two distinct periods 

 of male-production occurred, each preceded and followed by a 

 period of few male-producers. 



From each of these generations a number of female-producers 

 and sometimes also male-producers, were fixed in Bouin's fluid. 

 They were sectioned 5ju in thickness and stained with iron hema- 

 toxylin followed by eosin. 



