SEX-CHROMOSOMES AND INHERITANCE 183 



queen must transmit to him all her characters, thus giving 

 rise to a form of inheritance that has a superficial resem- 

 blance to sex-linked inheritance. A queen of a pure race, 

 bred to a male of another race with a dominant factor, 

 produces daughters all showing the dominant character 

 of the father, and sons all showing the recessive character 

 of the mother. Since the son gets his entire chromosome- 

 complex from his mother, he must necessarily be like her, 

 whether the character in question is in the sex-chromo- 

 some, or in some other one. 





<t?i;/;:'vvi<^.';.;:iS5 



a 



SSt'^ 



■mA 



m. 



mvm^!ffm^m 





Fig. 83. — Extrusion of the polar body from a male-producing egg with lagging chro- 

 mosomea on the spindle, a; and extrusion of the polar body from a female-producing 

 egg, 6; in Phylloxera. 



In the phylloxerans there are two parthenogenetic 

 generations followed by a sexual one ( Fig. 82 ) . In the sec- 

 ond parthenogenetic generation two whole chromosomes 

 leave certain eggs (Fig. 83) passing into the single polar 

 body which is given off from the egg. Such eggs have two 

 less sex-chromosomes and develop parthenogenetically 

 into males. In other eggs of the same generation all four 

 sex-chromosomes are retained after the polar body is 

 produced. These eggs also develop parthenogenetically, 

 but produce females. Similar changes take place no doubt 

 in the aphids, for the males have been shown to have one 

 less chromosome than the female, although the loss of one 



