RESPIRATORY METABOLISM. ~ 



as the culture bottles, and the two ends covered with white cloth 

 gauze, the flies tended to congregate under the gauze cover when 

 cylinder was placed in an upright position despite the fact that the 

 composition of the air in the cylinder was uniform throughout. 

 By changing the position of the culture bottles, as well as of the 

 wire gau/e cylinder, in respect to the source of light the flies could 

 IK- made to < ate at either end whether cotton plugs, gauze. 



t. .. were used as stoppers. It seems to the authors that factors 

 other than ventilation, doubtless light, are responsible for such be- 

 havior of the tlie- in differently stoppered bottles. 



RESPIRATORY METABOLISM. 



Siii' constitution of wild and vestigial >tork> di li'ers 



ally, u was deemed desirable to measure the rates of respira- 

 tory metabolism ( ,f the two types to see if in this rc-]>cct equally 

 marked dittYrenrc- could be detected. Such a comparison of i 

 piratoiy metabolism requires that all body movements, etc.. be 

 eliminated and that the organisms be under identical environmental 

 and ph\ sjologii a! conditions throughout the experiments. To 

 meet these requirements, in the present investigations, sterili/ed 

 pupa-, kept under identical conditions, have been used. Since rates 

 of respiratory metabolism are usually expressed per gram body 

 weight per unit of time, it was also necessary to weigh the organ- 

 isms ued in the experiments. The general methods used in ob- 

 taining pupal weights were as follows: Pupie of known age were 

 carefulh <1 from the filter paper by means of a thin metal 



spatula, cleaned and washed, then sterili/ed in 95 per cent alcohol 

 and again washed in water. The excess moisture was next re- 

 moved by placing the pupa,* on dry filter paper. They were then 

 weighed on a delicate analytical balance, in lots of five and ten 

 ami the avi 'gbt per pupa determined. 



Figure ; based on the weights of e \eral hundred individuals 

 show- graphically the average body weights for pupae of the two 

 -locks at different ages. It is evident from an examination of 

 this figure that vestigial pupae are somewhat heavier than wild and 

 remain -,, throughout their entire pupal life. Ycsiigials. how- 

 ex er. do not produce as many pupae as the wild. It is necessary, 

 therefore, in exj < its to have larger numbers of vestigial cul- 



