156 GENETICS AND EUGENICS 



are laid by the Fi females and segregation is seen first in the 

 eggs laid by F2 females. Spindle-shape of egg is a recessive 

 variant from normal, oval shape, and light brown egg-color 

 and gray egg-color are recessive variations from normal 

 slate-color. 



Bateson (1913) has brought together records for numerous 

 cases of unit-character color variation in moths and beetles 

 occurring in the wild state. These cases present nothing in 

 principle different from the variations of silkworms, but 

 show that Mendelian sports occur among insects "in nature" 

 as well as under artificial conditions. 



The most complete and in many respects the most instruc- 

 tive series of unit-character variations recorded in any insect 

 has taken place within a very few years in a small fruit fly, 

 Drosophila, while it was under observation in the Zoological 

 Laboratory of Columbia University. For this discovery we 

 are indebted to Professor T. H. Morgan and his pupils. 

 Drosophila melanogaster is a small fly with grayish brown 

 body and red eyes, which lays its eggs in fermenting fruits. 

 Apples, peaches, grapes or bananas with broken skin afford 

 good conditions for its multiplication. It is sometimes known 

 as the vinegar or pomace fly because the alcoholic fermenta- 

 tion of apple juice attracts it to vinegar jugs, pickle jars, and 

 cider mills. This fly while breeding in Professor Morgan's 

 laboratory produced a white-eyed sport, which lacked en- 

 tirely the normal red eye-color. The sport was first observed 

 in a male individual, which bred to normal mates produced 

 only normal offspring. But when these Fi offspring were 

 bred together they produced white-eyed offspring as reces- 

 sives in the expected proportion, one-fourth. Curiously 

 enough, however, all were males. Nevertheless, when these 

 obviously recessive white-eyed males were mated with Fi 

 females (heterozygotes) a generation was produced consisting 

 of white-eyed individuals and red-eyed individuals in equal' 

 numbers, and among both sorts the sexes were approximately 

 equal. White-eyed individuals bred together breed true, but 

 in crosses the white-eyed character seems to have a prefer- 



