192 APPENDIX 



for student guidance are for development at 25° C. At 

 lower temperatures development will be slower; tempera- 

 tures above 28° C. are very unsatisfactory. 



More experience in handling the flies will be gained by the 

 student if f^ies are drawn off and counted more frequently 

 than specified in the directions. However, unless all flies 

 are removed every twenty-four hours counting should not 

 be continued for longer than nine days because of possible 

 contamination with flies of the next generation. 



Virgin females can be obtained by isolating very dark, that is, 

 old pupse in vials containing a small piece of moist paper. 

 Be sure that no drop of water is in the vial to trap the 

 newly emerged adult. If it is desirable to keep flies obtained 

 from isolations longer than twenty-four hours they can be 

 fed drops of a solution of compressed yeast on the paper 

 in the vial. To obtain virgin females from stock cultures 

 remove all adults. Females that have emerged within ten 

 hours after clearing the stock bottle will be virgin. Breed- 

 ing stock obtained from culture bottles should be very 

 lightly etherized and full recovery checked before it is issued 

 to students. 



Students should be told that the abdominal pigmentation is 

 not strong on freshly emerged adults. This makes identi- 

 fication of sexes difficult. They should also be warned 

 about over-etherization, especially if a wing-length char- 

 acter is being studied. 



For etherizing bottles use ordinary wide-mouthed bottles 

 selected to coincide with the mouth size of the culture bot- 

 tles. Wrap a small amount of cotton in a piece of cheese 

 cloth and fasten it, with a nail or wire, to the inner end 

 of a cork which fits the etherizing bottle. Bottles should 

 be used clean and dry; the ether is applied to the cotton. 



One-fourth of a fresh cake of compressed yeast dissolved in 

 about 100 c.c. of water is concentrated enough for the inocu- 

 lation of culture bottles. Use two drops of this solution for 

 seeding bottles just before introducing the breeding stock. 



Six to eight pair matings can be made in running stock cul- 

 tures. Care must be exercised to keep stocks uncontam- 

 inated. 



