MALE-PRODUCTION IN HYDATINA 145 



Table 14 records the results of this experiment. There is 

 a small increase in male-production in the oxygen line. 



Another feature of the oxygen line that is perhaps of signifi- 

 cance in connection with the next experiment, is the distribution 

 of the male-producers in the family. In any Une of Hydatina 

 the male-producers tend to occur in groups; that is, several 

 successive members of a family will be male-producers. This 

 grouping is most apparent in Unes in which male-producers are 

 abundant; for, though the most frequent number of male- 

 producers in a group is always one, by far the majority of male- 

 producers in such a line occur in much larger groups. When 

 the proportion of male-producers is 30 to 40 per cent, it is not 

 uncommon to find groups of ten, twenty, or even thirty or more 

 male-producers occupjdng successive places in the family. The 

 cause of this grouping is unknown, but e'vidently when the con- 

 ditions are right for the appearance of male-producers, they 

 remain so for a time, then disappear or are inoperative. 



Were there no such grouping, in a line yielding only 5 or 10 

 per cent of male-producers, most of these would necessarily 

 occur in groups of one. Groups of two would be very uncom- 

 mon, while larger groups would be almost unknown. 



It is interesting, therefore, especially in view of the fact that 

 large groups are quite common in lines in which male-producers 

 are abundant, to compare the distribution of the male-producers 

 in the two lines of table 14, one having a higher proportion of 

 male-producers than the other. The daily records of these two 

 Hnes have been examined, and the number of times that one, 

 two, three, four, or five successive members of the family were 

 male-producers was recorded. There were no groups larger 

 than five. If such records are to be trustworthy, it is essential 

 that the order of individuals in the family be known. There is 

 a possibihty of error here, for the order of age was determined 

 each day by the order of size. In the young females the dif- 

 ferences in size usually left Httle doubt as to their relative ages, 

 but errors were undoubtedly sometimes made. However, 

 errors were no more probable in one line than in the other; 

 and there could have been no bias, either conscious or uncon- 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 21, NO. 1 



