August 16, 1907] 



SCIENCE 



217 



that the male and female sex characters form 

 an allelomorphic pair and undergo segrega- 

 tion in gametogenesis. 



In one of the goldenrod aphids all of the 

 parthenogenetie individuals are a deep red- 

 dish brown, the males are green and the 

 females brown, both males and females being 

 produced by the same mother. Assuming that 

 sex may be regarded as an inheritable char- 

 acter, the indications are that the partheno- 

 genetie individual is both a sex-hybrid and a 

 color-hybrid, green color and male sex being 

 recessive. In the sexual generation green 

 color becomes dominant with the male sex, 

 brown with the female. Here correlation of 

 color with sex, and selective fertilization, i. e., 

 only gametes containing opposite sex charac- 

 ters forming fertile unions, would account for 

 the conditions observed. 



In another aphid found on the star cucum- 

 ber, the parthenogenetie generations consist 

 of green and red individuals. Both red males 

 and green females are produced by the same 

 parthenogenetie mother which may be either 

 green or red. Here again it appears that all 

 of the parthenogenetie individuals must be 

 both sex-hybrids and color-hybrids, but either 

 color may be dominant during the partheno- 

 genetie generations with no evident determin- 

 ing factor. 



In an aphid which is abundant on the 

 flower clusters and upper leaves of (Enothera 

 biennis, we find more complicated conditions. 

 In the parthenogenetie generations there are 

 two colors, a dark red and a bright green. In 

 autumn certain red-winged mothers produce 

 red apterous females, and other apterous red 

 individuals produce greenish-brown males, 

 while red females and green males come from 

 the green mothers. The winged males are 

 produced only by apterous mothers, the apter- 

 ous females only by winged mothers. In this 

 case all may or may not be sex-hybrids and 

 color-hybrids. 



In November, 1905, I placed sexual forms of 

 these (Enothera aphids on (Enothera rosettes 

 in the greenhouse and an abundance of eggs 

 were laid. The eggs hatched early in March, 

 giving both red and green young. Indi- 

 viduals of the two colors were isolated on 



(Enothera plants protected with fine tarletan, 

 and the several families were kept under ob- 

 servation in the greenhouse until June 14, 

 about three months from hatching. All of 

 the members of each family remained true to 

 the color of their egg-ancestor. The plants 

 with the aphids were then taken to Cold 

 Spring Harbor and planted out under tarletan 

 screens. Syrphid larvae killed many of the 

 aphids. The last of the green ones disap- 

 peared in August, while some of the red ones 

 lived until the last of September. In no case 

 did any individual of any one of the families 

 deviate in color from its egg-ancestor. Sexual 

 forms did not appear before I left Cold Spring 

 Harbor on September 28. After returning to 

 Bryn Mawr, about October 1, I collected both 

 green and red parthenogenetie aphids from 

 wild (Enotheras and raised the males and 

 females of the sexual generation from these. 

 The males of g%een parentage are bright green 

 like their mothers, while the females are pale 

 green when born and gradually grow more 

 and more reddish until, when mature, they 

 are a bright red, not quite so deep a red, how- 

 ever, as that of the red females from red 

 mothers. The males of red parentage are red 

 when born, but change gradually to a greenish 

 brown, while the females are deep red like the 

 mothers, the red being a little brighter at 

 maturity than that of the parthenogenetie 

 generations, but easily distinguishable from 

 the brighter and more transparent red of the 

 females of green parentage. 



It will thus be seen that the color which 

 comes from the winter egg holds for all of 

 the parthenogenetie descendants, but when the 

 sexual forms appear the males are green or 

 greenish brovra, and the females red, indi- 

 cating some relation between color dominance 

 and sex. That this relation can not be asso- 

 ciated with different metabolic conditions in 

 the two sexes is shown by the fact that in the 

 star cucumber aphid, where there are both 

 green and red parthenogenetie , strains, the 

 color conditions in the sexual generation are 

 reversed, — the males are red and the females 

 green. 



A few preliminary experiments were made 

 in November, 1906, in mating males and 



