n8 



CYTOLOGY 



CHAP. 



9 





* 



I :; 



r * 



' ' 



B 



-' ' x 



f 





FIG. 54. 



The chromosomes in the life-cycle of Phylloxera fallax. (After Morgan, J.E.Z., 1909, and 1915 a.) 

 A, B, polar body formation in a 9 -producing parthenogenetic egg : all the chromosomes retained ; C, D, 

 polar body formation in a & -producing parthenogenetic egg, showing elimination of the X chromosome : 

 E, metaphase I., sexual egg ; F, chromosome group from a 9 embryo, twelve chromosomes ; G, chromosome 

 group from a $ embryo, ten chromosomes. 



p.b. polar body ; X, the (double) sex chromosome. 



