MALE-PEODUCTION IN HYDATINA 



141 



TABLE 11 



Showing the effect of rearing rotifers in the presence of Spirogyra. In one line the 

 parents of each generation were reared in dishes containing Spirogyra; in the 

 other line there was no Spirogyra in the parents' dishes. All offspring in both 

 lines were reared in the absence of the alga 



set in the sunlight. Bubbles, presumably of oxygen, were usually 

 present in the Spirogyra dishes, indicating that photosynthesis was 

 taking place. 



As indicated in table 11, there is a noticeable increase in the 

 number of male-producers in the Spirogyra cultures. 



Experiment 15. The preceding experiment was repeated, this time 

 with two lines in Spirogyra cultures, and but one control. The meth- 

 ods were the same as described for Experiment 14. Table 12 gives the 

 results. In these lines there is practically no difference between the 

 Spirogyra cultures and the control. 



Experiment 16. Adopting for this experiment Whitney's method 

 of rearing only the parents under experimental conditions, we used 

 the following procedure. Two or three mature, egg-laying females, 

 members of the same family, were placed in each of two dishes. In one 

 was placed some Spirogyra, in the other none. Both dishes were 

 put into a covered dish, which was floated on the water in a small 

 aquarium, and kept in the sunlight at a south window during the major 

 part of each day. A thermometer was put into the floating dish, 

 and the temperature (at this time often quite high out of doors) was 

 found to vary only two or three degrees during the day. After 24 

 hours the parents were removed. The eggs laid during this 24 hour 

 period hatched where they were laid, and the young were removed to 

 spring water to grow to maturity. These offspring are recorded in 

 table 13. In this experiment there is a slight reduction in the 

 number of male-producers, though it is so small as to be probably 

 insignificant. 



