1917 EXTOMOLOGICAL SOCIETY. 69 



= egg cell; S. sperm with an X chromosome. 



s = sperm without an X chromosome. 

 Z = zygote with two X chromosomes. 



z = zygote with one X chromosome. 



S s = male gametes. 



Female ) Z z .,r, , « •• i i 



gametes ] 7 = lL-\- 2z, givmg an equal number. 



Y\\ the second case where the female is heterozygous for sex and the male 

 homozygous, the chances in tertilization are again approximately, an equal number 

 of males and females. 



O = egg cell with an X chromosome, 

 o = egg cell without an X chromosome. 

 S ~ sperm cell with an X chromosome. 

 Z = zygote with t\to X chromosomes (male.) 

 z = zygote with X chromosome (female.) 



= male gametes. 



I I 1 = 2Z + 2z, an e 



gametes i | andfemales. 



Female 10 Z Z \ nn s >-, i 1 r 1 



,g > = 2Z + 2z, an eiual number of males 



IlEItEDITY IX THE ApIIIDS AXD BUCS, 



The life-history of aphid:^ is well known. The fertilized q^^^ hatches out a 

 female, the stem-mother, the following spring, followed by a succession of genera- 

 tions of females. On the approach of autumn a brood of sexual males and females 

 ajjpears. Tlic explanation of these phenomena is not clear, but some progress has 

 been made in clearing the mystery. Morgan has shown that the spermatids of 

 Phylloxera are of two kinds, but those containing no accessory chromosome de- 

 generates. Consequently only those containing an accessory chromosome take part 

 in fertilization, and the fertilized eggs produce females. The problem of the 

 production of the males parthenogenetically, however, at the approach of autumn 

 has not yet been solved. It is probable, how^ever, that external or environmental 

 factors are to some extent responsible. In P. carycucaulis one stem-mother gives 

 rise to the line ending in. sexual females, and another stem to the line ending in 

 tlie males. On tlie other hand in other species of Phylloxera and in many apliids 

 the same stem-mother nmv produce both lines. 



In this coniH'tliort ,1 is interesting to observe the production of males and 

 females among bees, wa-i>s and ants. It is well knowTi that fertilized eggs of the 

 queen bee produce femahs, and on fertilized eggs males. The mature egg has one 

 sex chromosome, consequently the nn'r" cell has but one, but when the egg is 

 fertili?>ed by a male cell and product Las ;wo sex chromosomes, characteristic of the 

 cells of a female bee. 



Foote "and Strobell have recently mnde interostiiig studies of two species of 

 Euschistiis. The male of rariolarius has a Avell-defincd black circular dot on the 

 sixth segment of the abdomen, but in both sexes of sercus, the other species, the 

 spot is absent. When a female variolariiis was crossed with a male seruiis many 

 of the Fi hybrids showed the spot. Again, the cross between a pure male 

 rariolarius and the Ft female and spot appears. In the F= generation some speci- 

 mens showed the spot, wliile others did not. A satisfactory cxplanaMon of ihc 

 inheritance has not yet been given. 



