ii5 CYTOLOGY chap. 



intact to one pole, so that in anaphase I. there are three chromosomes 



/ 



B 





N 



If 



/ 







\o 



^y 



Fig. 53. 



<L^ 



'^ 



■'A 



Q 



The chromosomes in the life-cycle of Aphis saliceti. (After von Baehr, LC 1912^) A, spermatogonial 

 prophase; B, primary spermatocyte, beginning of the meiotic phase; C, D, E F, G, evolution of the 

 definitive chromosomes. Note the two bivalents and the single X chromosome. H, metaphase 1. ; 1, ana- 

 phase I • T K, telophase I. All the chromosomes now alike, all being miivalent and spht m preparation tor 

 the second division. L, resting stage between the two divisions ; M prophase II. ; N, metaphase H- J O, 

 telophase II. (N and O illustrate the case of the spermatocyte II., which contains the X chromosome.) F, ceii 

 from a segmenting egg with five chromosomes {i.e. a i);Q, cell from an embryo with six chromosomes {i.e. 



a $). 



p, plasmosome ; X, the sex chromosome. 



(2+X) at one pole and only two chromosomes at the other, in the 

 famihar manner. When cell division takes place, however, this is unequal. 



