462 N. M. Stevens 



In both Diabrotica soror and Diabrotica 12-punctata the small 

 heterochromosomes are usually quite closely associated with the 

 larger one (x) in the growth stages, but this is by no means invari- 

 ably true. It is not at all unusual to find them separated in some 

 cells and in one individual it was noted that the two were more 

 often widely separated. (Figures to illustrate this have been 

 thrown out for lack of space.) 



Fig. 73 shows a metaphase of the first spermatocyte from the 

 one individual of this species which had four small chromosomes. 

 Figs. 74 and 75 are anaphases from the* same section, from an 

 individual with two small chromosomes, showing in one case (Fig. 

 74, Si and So) both dividing, in the other (Fig. 75) one dividing (j-j) 

 and the other (si) passing undivided to the same pole with the odd 

 chromosome (x). In general, these small chromosomes are remark- 

 ably uniform in size. One case, however, was found among the 

 aceto-carmine preparations where an unusually small one was 

 constant for the individual (Figs 76-78). This very small chro- 

 mosome was not found dividing in the first spermatocyte and it 

 could not be followed in the second division. In one cyst the 

 spireme was segmenting, later than usual, into dumb-bell shaped 

 bivalents (Fig. 77), as in Tenebrio molitor (Stevens '05, PI. 6, 

 Figs. 177-179). 



As in the other species of Diabrotica it has not been possible to 

 find favorable stages for counting the chromosomes in the female. 

 One may be able to do this by breeding the insects and w^orking 

 with the tissues of the larva or pupa. Judging from similar cases 

 where the female number is known (for the Coleoptera, Elater I, 

 Fig. 229, PI. 13, Stevens '06, and Photinus pennsylvanicus, figures 

 not yet pubhshed; Anasa tristis and other Hemiptera, Wilson '05 

 and '06; Pceciloptera, Fig. 283, PI. 8 and Fig. 294, PI. 9, Boring 

 '07), we must suppose that the female number for Diabrotica 

 vittata is twenty-two and for Diabrotica soror and Diabrotica 12- 

 punctata, type I, twenty. Since the small heterochromosomes 

 seem to be as likely to go to the spermatozoa which receive the 

 odd chromosome (x) as to those which lack it, it would appear 

 probable that the conditions with reference to the small hetero- 

 chromosomes in the female are the same as in the male, and more- 



