Studies on Chromosomes 5 



Harmostes, etc., or the small pair of ordinary chromosomes of 

 Coenus and Euschistus, described beyond) or especially large ones 

 such as the largest pair in Alydus, and in some of the species of 

 Euschistus. Those of intermediate size are also obviously paired 

 in some of the forms (e. g., in Protenor, Fig. i); but in many of 

 the species the several pairs are not sufficiently marked in size to 

 admit of certain recognition. Nevertheless, a comparative study 

 of many species has convinced me of the correctness of the con- 

 clusion, first indicated by Montgomery ('01) and afterward more 

 fully worked out by Sutton ('02), that all the chromosomes (again 

 with the special exceptions referred to above) may be thus paired, 

 and that the chromosome-group as a whole includes two parallel 

 series of chromosomes that undoubtedly represent respectively 

 the descendants of those that originally are brought together in 

 the union of the gametes. This is very clearly brought out by 

 making camera drawings of the chromosomes, and arranging 

 them as nearly as practicable in pairs of equal size. This arrange- 

 ment conspicuously shows the sexual differences, as may be seen 

 by a comparison of Figs. 2, /and b (Anasa) and 5, c and g (Lygaeus). 

 There is, of course, a large error to be allowed for in the series 

 as thus arranged, and no pretense to complete accuracy in the 

 selection of the members of most of the pairs can be made. 

 Nevertheless, when all due allowance for differences of form, 

 foreshortening and the like is made, the fact that such a double 

 series exists is unmistakable. When it is borne in mind that the 

 spermatid-nuclei in each case contain a single series of chromo- 

 somes showing the same size-relations (cf. for instance, Figs. I, b, 

 <:, d; 2, a, d, e; 3, a, e, f; 4, b, /, d, /?), it becomes in a high degree 

 probable that the corresponding pairs of the somatic groups con- 

 sist each of a paternal and a maternal member, in accordance 

 with Montgomery's original and fundamental assumption ('01). 

 As may be seen by a comparison of the figures, the members of 

 each pair when in their natural position, do not as a rule lie in 

 juxtaposition but may occupy any relative position. Only at 

 the period of synapsis do they actually couple, two by two, to 

 form the bivalents whose members are subsequently separated 

 by the reducing division. 



