ii8 



CYTOLOGY 



CHAP. 



m 



.♦••• 



•••*. 

 »-•' 



,<• 



* 



B 



X. 





xb- 



^^.. 



X 



# 



r 



-•'^'^ 





# 



i 



J<- 



^ 



V' 



i 



Fig. 54. 



The chromosomes in the life-cycle of Phylloxera fallix. (After Morgan, J.E.Z., 1909, and 191 5 a.) 

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

 polar body formation in a <5 -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 (5 embryo, ten chromosomes. 



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



