THE INHERITANCE OF ABNORMAL VENATION. 



Practically all the experimental studies of inheritance have extended 

 through but few, rarely more than 6, generations and have been con- 

 cerned with pairs of non-intergrading characters. In the present work 

 more than 70 generations have been reared. This was possible for two 

 reasons: Drosophila ampelophila Loew has a very short life-history, 

 and it can be kept breeding throughout the year. The character 

 abnormal wing-venation, the inheritance of which was studied, may 

 be made to exhibit extreme variability, passing from less venation than 

 normal through normal to extra venation, so great that the additional 

 veins almost equal the normal in extent. 



At the Boston (1907) meeting of the International Zoological Congress 

 a preliminary report was presented upon this subject, 6 generations 

 having been obtained. During the summer of 1908 a report upon the 

 work (covering about 25 generations) done at the Station for Experi- 

 mental Evolution was submitted to the Director, but I deferred publi- 

 cation because I wished to test more in detail certain points, especially 

 sexual selection and the further fate of the abnormal strains. This 

 additional work was done at the American Museum of Natural History. 

 Incidentally I obtained confirmation of the previous work, but for the 

 most part the present paper includes only the Cold Spring Harbor data 

 and the conclusions drawn are as given in the 1908 report, except where 

 otherwise indicated. 



MATERIAL AND METHODS. 



Drosophila ampelophila (the small red-eyed "pomace-fly") is very 

 common about cider-mills, ripe fruit, vinegar-barrels, and the like. 

 The larvae normally live in the pulp of rotting fruits, especially during 

 the acetic-acid stage of decay. They will, however, thrive on the side 

 of a tumbler containing fruit-juices, and I have reared them through 

 several generations on stale beer. At a temperature of 25° C. the eggs 

 hatch in 40 hours or less. The duration of the larval period is, on the 

 average, 5 days, 2nd of the pupal period 4§ days. The adults become 

 sexually mature about 48 hours after emergence when kept at this tem- 

 perature. They live for about 3 weeks. The mean number of eggs is 

 close to 200. Copulation is repeated and frequent. 



Most of the flies discussed in this paper were bred in an incubator, 

 where an average temperature of 25.5° C. was maintained. A thermo- 

 graphic record was kept. Since the temperature of the incubator was so 

 nearly that of the working-room, absolute constancy was not obtained. 



The amount of variation is shown in fig. 1, which gives the frequencies 



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