BEHAVIOR. 



11 



DURATION OF COPULATION NECESSARY. 



As shown above, the length of time pairs remain mated is charac- 

 teristic for each species, ranging from about a minute in Drosophila 

 lutzii to about an hour in D. immigrans. The usual time for D. 

 melanogaster is about 21 minutes. I have conducted a few experiments 

 with this species, to see how long a time is necessary. Nine pairs 

 were mated, in each case using a male with a dominant mutant char- 

 acter, so that any offspring produced could be identified as his and 

 not due to a previous mating. These pairs were allowed to mate, 

 and were then shaken apart after a few minutes. The females were 

 then isolated to see if they would produce offspring. In no case was a 

 complete count of the offspring made, so that the figures given in 

 table 1 represent only minimum numbers. Evidently 8 minutes is 

 about the time required. 



