454 M - R - CLARE. 



third days of pupal development that the standard metabolism 

 of larvae is actually somewhat greater than that of the flies 

 although, relatively to body weight, the two stages may be more 

 nearly comparable. 



Before turning from the general subject we have been con- 

 sidering, a point of difference between the metabolism curves 

 for the first and second experimental periods should be noted. 

 For a cultural temperature of 25 C., we have seen that marked 

 fluctuations occur in rates of oxygen consumption among lots 

 of pupae derived from a single mating, and corresponding in a 

 very rough way with variations in pupal weight. In material 

 representing the first experimental period at a lower temperature, 

 the extent of fluctuations in metabolism is less pronounced until 

 the last day when it becomes increased. Pupal weights of the 

 first period are more irregular than for the second period and in 

 consequence the parallelism between weight and metabolism 

 tends to become lost. The relationship between pupal weight 

 and metabolism for this period is represented in Fig. 4. 



INFLUENCE OF SEX ON METABOLISM. 



It has been pointed out that for any one day of pupal life the 

 metabolic rates for different samples of pupae vary considerably 

 and that weight is a very untrustworthy guide in arriving at an 

 understanding of this irregularity. Is sex a contributing factor? 

 Biological literature abounds in references to the physiological 

 distinctness of the sexes and several important recent researches 

 have depended for interpretation on the postulate that male 

 animals possess a higher rate of metabolism than do female. 

 So far as the writer knows, only one experimental attempt has 

 been made to measure this supposed difference directly, namely, 

 the investigation by Benedict and Emmes (1915). With human 

 subjects these workers found a slight increase in metabolism in 

 favor of males over the rates for females. 



There are certain facts at hand to suggest a possible difference 

 in metabolism between the sexes of Drosophila. At times, at 

 least, there is a well developed tendency for female flies to 

 emerge earlier than the males from the first-formed pupae. The 

 present data happen to be inconclusive on this point. The 



