296 



A. FKANKLIN SHULL 



At least one generation in advance of each of the periods of 

 male-producers there should, according to Hertwig's Kernplasma- 

 relation theory, be an increase in the volume of the nucleus rela- 

 tive to the volume of the cytosome. The results bearing on this 

 question are described in a later section of this paper. 



Age of individual. A number of young females, each in a 

 dish by herself, were divided into three lots. In one lot the fe- 

 males were removed as soon as they began to lay eggs. If the eggs 

 were large enough to be probably female eggs, the mothers were 



TABLE 1 

 Showing the number of 7nale-producing (cf 9 ) and female-producing (99) indi- 

 viduals of Hydatina in random lots taken from the middle of the families of a 

 'semi-pedigreed^ line for nineteen generations. In this time there were two periods 

 of relatively high male-production 



DATE OF ISOLATION 



January 16 



19 



22 



25 



28 



30 



February 2 



5 



9 



12 



BATE OP ISOLATION 



February 15 



18 



21 



24 



27 



March 2 



5 



8 



11 



NUMBER 

 OFcf 9 





 

 

 

 17 

 13 

 6 



NUMBER 

 OF 9 9 



47 



48 

 13 

 35 

 21 

 27 

 29 

 36 

 42 



fixed, all together in one vessel in Bouin's fluid. The offspring 

 hatching from their eggs were subsequently examined to ascertain 

 that the mothers had all been female-producers. If any of them 

 had turned out to be male-producers, the whole lot would have 

 been discarded after fixation, but this precaution proved to be 

 unnecessary. The females of the second lot were removed from 

 thirty-six to forty-eight hours after egg-laying began, at which 

 time they could be certainly recognized as female- or male- 

 producing. Only the female-producers were fixed. The female- 

 producers of the third lot were fixed just before the end of the 

 egg-laying period, three or four days after they became adult. 



