44 2 M - R- CLARE. 



were never more than 20 hours old. The pairs of flies were 

 cultured in shell vials (about 9 cm. long by 2 cm. diameter) 

 containing banana agar and were transferred each day to fresh 

 vials so that the pupae forming in a particular vial resulted from 

 eggs deposited therein on a single and known day. A complete 

 cultural record was kept which included figures for the sex ratios 

 of the flies appearing in all of the vials in order that a check 

 might be had on any conditions of metabolism attributable to 

 sex peculiarities of the matings. It happened, however, that for 

 all of the matings the distribution of the sexes remained normal. 

 Some of the matings were cultured at variable room temperature, 

 ranging from 21 C. to 25 C. about a mean of 23 C.; others 

 were cultured in an incubator at a constant temperature of 25 C. 

 It is necessary to stress this distinction, for upon it will be based 

 a natural division of the data into two parts. Hereafter, the 

 pupse formed at room temperature will be referred to as of the 

 "first experimental period," whereas those formed at 25 C. 

 will be referred to as of the "second experimental period." 



The banana-agar was prepared according to the usual method 

 and while still liquid about 5 or 6 cc. of the material were intro- 

 duced into each previously sterilized vial, which was provided 

 with a cotton plug. Usually a sufficient number of vials was 

 prepared at a time to supply requirements for two or three days 

 and kept in a refrigerator while awaiting use. Before introducing 

 a pair of flies into a fresh vial, a small amount of powdered 

 Magic Yeast was dusted on the surface of the culture medium 

 and on this was placed a disc of towel paper cut somewhat 

 smaller than the bore of the vial. When a very limited amount 

 of paper is placed in a vial, the larvae developing therein pupate 

 on the glass without "spinning" and therefore require a minimum 

 of cleaning in preparation for use. They can then be removed 

 quite readily from the glass without danger of injury with a 

 small brush after a preliminary wetting with water. 



Whenever possible, the first 10 pupae appearing in a vial were 

 used for a determination, but quite frequently only a smaller 

 number could be secured. Each evening the vials for the 

 several matings were examined and any pupa which had appeared 

 unduly early was checked with a wax pencil in order that it 



