456 A^. M. Stevens 



the eastern species; and in the summer and autumn of 1907, 100 

 males of each species were studied by means of aceto-carmine 

 preparations. The character of the chromosomes in the male 

 germ-cells of the two species is precisely the same. About 50 

 per cent of the individuals examined have nine equal pairs of chro- 

 mosomes and an unpaired heterochromosome, while the remain- 

 ing 50 per cent have one, two, three or four additional small hetero- 

 chromosomes. 



DIABROTICA SOROR 



Type I 



The stages in the spermatogenesis of the first type are in most 

 respects similar to those of Diabrotica vittata. The sperma- 

 togonial metaphase has nineteen chromosomes (Fig. 17), the 

 unpaired chromosome (x) being the largest The synizesis and 

 synapsis stages are similar to those of Diabrotica vittata, but less 

 conspicuous in sections and the stages are less clear. The 

 changes that occur between the telophase of the last sperma- 

 togonial mitosis and the pale spireme stage (Fig. 18) prob- 

 ably take place much more rapidly in this species. A polar view 

 of the metaphase of the first spermatocyte division is shown 

 in Fig. 19, a lateral view in Fig. 20, and a late anaphase in Fig. 

 21. The odd chromosome is usually found at or near one pole of 

 the spindle in the metaphase (Fig. 20). The bivalents are similar 

 to those of Diabrotica vittata, and the first division separates 

 their univalent components. In preparations from Hermann 

 material the chromosomes of the daughter plates (Figs. 22 and 23) 

 often begin to show a vesicular condition and in telophase the 

 heterochromosome {x) forms a vesicle by itself, while the other 

 nine chromosomes are blended together (Fig. 24). Fig. 25 is 

 a later stage taken from a cyst in which some second spermatocyte 

 spindles were present, while Fig. 24 was from a cyst containing 

 a few first spermatocyte spindles. Half of the nuclei in these cysts 

 of course contain no heterochromosome. The rest stage between 

 the two divisions is more pronounced than in Diabrotica vittata 

 where the chromosomes are simply massed together in telophase, 



