IV 



THE SEX CHROMOSOMES 



103 



• • 





\ 



rr Ji 



M!/^.. 



\ \ 



^ 





H 



The 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. 



Group. 



Neuroptera . 



Orthoptera . 



Coleoptera 



Diptera . 



Hemiptera heteroptera 



Hemiptera homoptera 



Total 



Number of Species in which the Rcductional Division for 

 the Sex Chromosomes is the 



First Division. 



I 



88 



38 

 II 



2 



43 



183 



Second Division. 



I 

 O 



2 

 O 



68 

 I 



72 



