344 Aaron Franklin Shnll 



By September ii, the same female had laid several small eggs, 

 also with comparatively thin shells. On September 12 there were 

 23 small eggs in the dish; no more were laid. On September 13, 

 a numberof males were swimming in the dish, and some of the small 

 eggs were then only empty shells. Fifteen males in all appeared 

 in the dish, the last two on September 16; the remaining eight' 

 small eggs did not hatch. 



On September 21a young female was found in the dish, and one 

 of the large egg shells was broken and empty. The other large 

 egg had not hatched Dec. 17, when it was discarded. 



Thus, winter eggs and male eggs were secured from the same 

 parent. Since so far as known all the p^rthenogeneticeggsof one 

 individual are of the same sex, there seems to be little room to 

 doubt that wmter eggs are male eggs that have been fertdized. 

 The bearing of this is pointed out elsewhere. 



SUMMARY OF RESULTS 



The proportion of male-producers in Hydatina senta may be re- 

 duced, even to zero, by rearing the rotifers in the water of old food- 

 cultures, from which the protozoa have been removed. This 

 effect is due to substances dissolved in the water. If, instead of 

 being reared in the water of old food cultures, the rotifers are bred 

 in spring water but fed from old cultures and not fresh ones the 

 proportion of male-producers may be likewise reduced, but in 

 less degree. 



Starvation may be accompanied by a higher proportion of male- 

 producers; but this is probably due to the reduced amount of dis- 

 solved substances incidentally introduced with the food. 



No evidence of so-called "sex-strains" has been found; more or 

 less constant differences attributed to "strains" may have been 

 due to the use of food cultures containing different quantities of 

 dissolved stuffs. 



Families bred from the last daughter of a family include on the 

 average fewer male-producers than families bred from the first 

 daughter. This may be due to the accumulation of substances 

 in the water in which the parent was reared. 



