CELL INCONSTANCY IN HYDATINA SENTA 



459 



The commonest aberrant numbers are seven and nine, while 

 the extremes show a reduction of 37.5 per cent below and an 

 elevation of 25.0 per cent above the usual number (eight). 



To discover whether anything in the environment caused these 

 differences in the number of nuclei, or whether any relation be- 

 tween the deviation and other phenomena could be established, 

 all recorded facts were carefully examined. Information was 

 found concerning the following points : 1) Some of the two hundred 

 and forty-five rotifers examined belonged to periods of many 

 male-producers, others to periods of few male-producers; 2) some 

 were young, some middle-aged, some old females ; 3) some were 

 reared in spring water, others in manure solution; and 4) some 

 were male-producers, others female-producers. In each of these 

 groups some aberrant yolk glands were found. How frequently 

 the unusual numbers occurred under the several circumstances 

 named, is shown in tables 2, 3, 4 and 5, respectively. 



The numbers of specimens aberrant with respect- to the num- 

 ber of nuclei in the yolk gland are, of course, too small in any of 



TABLE 2 



Distribution of individuals of Hydatina senta having aberrant numbers of nuclei 



in the yolk gland, with reference to periods of many male-producers 



and periods of few male-producers 



TABLE 3 

 Distribution of individuals of Hydatina senta having aberrant numbers of nuclei 

 in the yolk gland, with reference to the age of the individuals 



