NUCLEAR VOLUME AND LIFE-CYCLE OF HYDATINA 293 



In view of this strong support of the Kernplasmarelation theory 

 from responsible quarters and its widespread application to a 

 variety of phenomena, it seemed desirable, when opportunity was 

 offered to test it in one of its phases in an animal that afforded at 

 least a chance of separating causes from effects or inconsequential 

 events, that such opportunity be embraced. Hydatina seems to 

 present the requisite material, for reasons stated below. 



HYDATINA AS MATERIAL FOR THE STUDY OF THE KERNPLASMA- 

 RELATION IN A PARTHENOGENETIC ANIMAL 



The life-cycle of Hydatina senta is more accurately known 

 than that of any other animal exhibiting its type of partheno- 

 genesis. There is no longer any disagreement among recent in- 

 vestigators regarding the effectiveness of external conditions in 

 altering the life-cycle. Moreover, the precise point in the cycle 

 at which the external agents are effective is knowTi. It has been 

 sho-^Ti (Shull, '12) that artificial modifications of the cycle must 

 occur in the growth or maturation period of the egg. 



There are, moreover, at least three independent ways in which 

 the Kernplasmarelation may be connected with changes in the 

 life-cycle if Hertwig's views are correct. First, many lines of 

 rotifers show a marked periodicity (Shull, '15) in the production 

 of males, periods of many male-producers alternating with 

 (usually) longer periods of few male-producers. The ratio K/P 

 should change with these alternating periods. 



Second, male-production is related to the age of the parents 

 (Shull, '10). The first eggs laid by a female yield relatively few 

 male-producers; the number of male-producers in the family 

 increases gradually up to the middle of the family, at which time 

 they are three or four times as common as at the beginning, and 

 then they become gradually less frequent to the end of the family. 

 There should be a corresponding change of the Kernplasmarela- 

 tion during the lifetime of the parent. 



Third, external agents profoundly alter the number of male- 

 producers. Manure solution, one of the most effective of the 

 agents that repress the sexual phase, may easily exclude male- 

 producers altogether. Animals reared in manure solution should. 



