4 David Day Whittle y 



and a few rotifers put into it. The jar was covered so as to pre- 

 vent evaporation of the water. Rotifers have lived in it to this 

 time, April, 1907, although no more food material has ever been 

 added. It is absolutely necessary that the surface of the water be 

 free from a scum for the rotifers will die within a few hours if it 

 is present. It is safer, in order to keep the surface free, to tie the 

 horse manure in a muslin cloth and place it in a well covered jar 

 nearly filled with water. 



Ill INFLUENCE OF TEMPERATURE 



I Maupas^ Experiments 



The experiments of Maupas were so briefly described that it is 

 very difficult to understand clearly how he obtained his results. 



Nussbaum and Punnett are inclined to believe he determined 

 that a female was a male-laying or a female-laying individual 

 by the size of the eggs that she produced. Small eggs being 

 assumed always to give rise to males while larger eggs give rise to 

 females. Nussbaum has measured a series of both male and 

 female eggs and found that in some instances the two kinds of 

 eggs over-lap in size. Thus he points out an error through which 

 Maupas' results might have been obtained. 



Isolating and counting the eggs of this rotifer would be exceed- 

 ingly tedious and require almost constant attention. As the sexes 

 can be readily distinguished at any period and as it requires only 

 36 to 48 hours for a female to mature and produce eggs it seems 

 to me extremely probable that Maupas must have allowed some 

 at least of the eggs to hatch before recording his results. 



As his experiments are so few and briefly described it may be 

 well to present them here in order that they may be compared 

 with and interpreted by my own. Experiment I. Lot A, tempera- 

 ture 26° to 28° C. Five female-laying female sisters produced 104 

 eggs; 97 per cent developed into male-laying females. Lot B, 

 temperature 14° C. Five other female-laying females, which 

 were sisters of lot A, produced 260 eggs; 5 per cent developed into 

 male-laying females. 



