CROSSING TWO HEMIPTEROUS SPECIES. 229 



sex. This would place sex-linked factors for the testes in the X- 

 chromosome of these insects; and locating these factors in this 

 chromosome would involve their being in the female-producing 

 spermatozoa only, and this type of spermatozoa therefore would 

 carry the determining factors for both the ovaries and the testes, 

 while the male-producing spermatozoa would carry neither the 

 one nor the other. We shall try to show by an analysis of the 

 chromosomes that it is as impossible to associate the testes 

 with the sex-chromosomes as we have shown by experiment is 

 true for the two other exclusively male characters the genital 

 spot and the intromittent organ. In order to simplify the dis- 

 cussion, we reproduce the following diagram used in an earlier 

 paper to show the method of division of the 14 somatic chromo- 

 somes which are distinctive of both E. variolarius and E. servus. 

 In the diagram we have used the method of designating uni- 

 valents by the letters of the alphabet, bivalents being represented 

 by AB, CD. EF. 



Sp. Tid. 



Second Sp. Cyte Chromosomes. 



Chromosomes. A C E X - 9 



First Sp. Cyte 



Chromosomes. ^~A C E Y cf 



A B C D E F X Y 



B D F X 9 



D F Y C? 



Scheme of the two maturation divisions of Euschistus variolarius and Euschistus 

 servus based on the assumption that the first maturation division separates auto- 

 somes of maternal and paternal origin and the second division halves .them. The 

 .XTF-chromosomes on the contrary being halved in the first division and separated 

 in the second division. The relative positions of the autosomes may be changed 

 unless definite chromosomes are always destined to the same pole, but reversing 

 their position in this regard does not alter the end result that the only chromosome 

 common to both so-called male-producing spermatids is the F-chromosome. 1 



The above diagram demonstrates the two types of spermatozoa, 

 those having the X-chromosome so-called female-producing; 

 and those having the Y-chromosome so-called male-producing. 

 If we accept Morgan's conclusion that factors determining all 

 sex-linked characters are located in the X-chromosomes and we 

 assume that the primary sexual characters are sex-linked, this 

 involves placing the factors determining both the ovaries and the 



1 Only six of the twelve autosomes are designated. 



