360 • A. H. STURTEVANT 



in all the similar experiments here reported care was taken to 

 have the competing flies as nearly the same age and size as pos- 

 sible. The result indicates that there is very slight, if any, 

 selection against the clipped males. It seemed possible that 

 courtship made the female ready to copulate, but that she 

 would then mate with either male. To test this hypothesis 

 another series of experiments was carried out. A single pair 

 of flies was placed in each vial, using each day an equal number 

 of normal and of clipped males. The length of time before 

 copulation was recorded in each case. A preliminary account 

 of this experiment has been published by Morgan ('13); but the 

 data used there have been discarded, since two serious sources 

 of error had not then been recognized. It was not realized 

 that the time before copulation might be influenced by a pre- 

 vious copulation having occurred in the same vial ; and sufficient 

 precautions against drying were not taken — a very important 

 factor. A new series of experiments, in which these points were 

 controlled, gave the results shown in table II. As a matter of 

 fact, however, these data are very similar to the discarded series. 



TABLE II 



Minutes Number of times observed 



before 



Copulation Normal <-? Clipped r? 



0- 3 15 4 



4-6 19 9 



7-9 10 7 



10-12 15 5 



13-15 3 7 



16-18 8 4 



19-21 3 10 



22-24 3 4 



25-27 9 4 



28^30 2 2 



31-33 2 2 



34-36 4 



37-39 1 2 



40-42 3 2 



43-45 2 1 



46 and over, including failures. 43 73 



This table seems to justify the suspicion that led to the ex- 

 periment. Had the females discriminated against the clipped 

 males to the extent shown above when both kinds were present, 

 the normal males would certainly have appeared at a greater ad- 

 vantage. That the result was not due to less activity on the part of 

 the clipped males is indicated both by the contests described above 



