14 Edmund B. Wilson 



d. Harmostes reflexulus 



My material of this species is much less abundant than that of 

 the three preceding, and the preparations are not of the same 

 excellence. They nevertheless show beyond doubt that the num- 

 bers are here the same as in Protenor and Alydus, viz., thirteen in 

 the male and fourteen in the female. In my sections of both sexes 

 the chromosomes appear less regular in contour than in the other 

 species examined (probably owing to somewhat defective fixation). 

 They show clearly, however, in both sexes a largest pair and a 

 smallest (m-chromosomes), as in the other forms. 



C. Second Type. Forms Possessing Unequal Idiochromosomes 



The sexual differences of these forms have been worked out in 

 Lygaeus turcicus, five species of Euschistus (variolarius, ictericus, 

 tristigmus, fissilis and servus), Coenus delius and Podisus spinosus. 

 In the last named species the unreduced number is sixteen, in the 

 others fourteen. In all, the number of chromosomes is the same 

 in both sexes, but while the males show a large and a small idio- 

 chromosome, the females show two large idiochromosomes that 

 are equally paired. This difference clearly appears in all the 

 species examined but is most conspicuous in Euschistus vario- 

 larius, E. ictericus and Lygaeus turcicus, where the inequality 

 of the idiochromosomes is most marked. The relative size of 

 the idiochromosomes varies somewhat (perhaps owing to differ- 

 ences in the degree of extraction of the dye) but on the whole is 

 characteristic of the different species, as described below. 



In all of the species of Euschistus examined, and in Ccenus 

 delius, a largest and a smallest pair of ordinary chromosomes 

 (the latter marked s in some of the figures) are readily distinguish- 

 able. These give rise to corresponding large and small bivalents 

 in the first mitosis, and are recognizable as single chromosomes 

 in the spermatid-groups (Figs. 4, 5). The small chromosomes 

 are in every case smaller than the large idiochromosome, and in 

 Mineus bioculatus (Fig. 4, /?, q) are actually smaller than the small 

 idiochromosome. It is possible -that this pair of chromosomes 



