IV 



THE SEX CHROMOSOMES 



103 



Ihe chromosomes of the beetle Blattella germanica. (Stevens, Carnegie Inst. Pub., 1905.) A, primary 

 spermatocyte ; B, prophase I. ; C, metaphase I., polar view, showing twelve chromosomes, X not distinguish- 

 able from the others in this view ; D, portion of metaphase I., side view, showing X passing undivided to one 

 pole ; E, late anaphase I. ; F, telophase I., X in one daughter nucleus only ; G, prophase II. of the secondary 

 spermatocyte which contains the X chromosome ; H, polar view of metaphase II. of secondary spermatocyte 

 lacking the X chromosome ; I, similar figure of secondary spermatocyte containing the X chromosome ; 

 J, side view of metaphase II., showing the X chromosome dividing. 



cases which are doubtful or which present any special complication have 

 been omitted. 



