58 



SCIENCE 



[N. S. Vol. XXIX. No. 732 



Spermatocyte 



Division Spermatozoa Egg 



Actual 

 Somatic 

 Number of 

 Zygotes Chromosomes 



Thyanta 



Syromastes 



(^ 22 



%24 



+ 



+ 



Gelastocoris 



^35 



%3S 



Ordinary chromosomes — unshaded. 

 x element — ^blaek. 

 y element — with cross-bars. 



panying diagrams.* Half of all tlie sper- 

 matozoa thus receive the X-element, while 



* These diagrams are from my own observations 

 with exception of those of Gelastocoris (from 

 Payne). For the sake of simplicity and ready 

 comparison all the forms are represented with 

 but four pairs of ordinary chromosomes (in 

 white), all with the same size-relations and group- 



the other half may receive a Y-element in 

 its place, though this may be absent. 



Comparison of the male and female so- 

 matic chromosome-groups proves, indirect- 

 ing. The X-element is in each case black, the 

 Y-element cross-barred. The actual numbers of 

 the chromosomes are given for each sex at the 

 right. 



