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THE AMEBIC AN NATURALIST [Vol. LII 



to develop, that they produce fewer young per day, and 

 that these young are on the average smaller than in the 

 case of wingless females. 



There are certain objections, however, to the foregoing 

 conclusion. First, if winged viviparous females have a 

 low metabolic rate while the wingless ones have a high 

 rate, during the parthenogenetic portion of the cycle a 

 parent with high rate of metabolism produces chiefly off- 

 spring with a low rate of metabolism, and vice versa; 

 for wingless females produce chiefly winged ones, and 

 winged females produce chiefly wingless ones. On the 

 other hand, in the sexual part of the cycle, parent and 

 offspring are both of the same metabolic type ; for winged 

 females (with low rate of metabolism) produce mostly 

 sexual females (which in accordance with Riddle's view 

 should possess a low rate of metabolism), whereas wing- 

 less females (high rate) produce mostly males (high 

 rate). Why parent and offspring should be of a similar 

 type of metabolism in the sexual phase, but of unlike type 

 in the parthenogenetic phase, is not clear. 



Unless the withholding of food increases the rate of 

 metabolism, or unless the rate of metabolism is taken to 

 mean not the absolute rate, but the rate relative to the 

 food consumed, another objection to the assumption that 

 the winged female possesses a lower rate of metabolism 

 than the wingless ones is found in the work of Miss 

 Gregory ( 1917 ) . Miss Gregory finds that in Microsiphum 

 destructor starvation of the apterous mothers results in 

 the production of more winged offspring. It is only by 

 assuming that starvation increases the rate of metab- 

 olism, or that "rate of metabolism " means the relative 

 rate— rate relative to the amount of food consumed, not 

 relative to the rate in another type of individual that 

 Miss Gregory's discoveries can be interpreted in support 

 of Riddle's hypothesis; providing, of course, that the 

 winged females have a lower metabolic rate than the 

 wingless females. 



If, to avoid either or both of the difficulties just men 



