102 ETHEL NICHOLSON BROWNE 



Stevens, N. M. 1911 Further studies on heterochromosomes in mosquitoes. 



Biol. Bull., vol. 20. 



1912 a Supernumerary chromosomes and synapsis in Ceuthophilus. 

 ■ Ibid., vol. 22. 



1912 b Further observations on the supernumerary chromosomes and 



sex ratios in Diabrotica soror. Ibid. 

 Vejdovsky, F. 1911-12 Zur Problem derVererbungstrager. Kon. Bohm.Gesel. 



d. wiss. Prag. 

 Wilson, E. B. 1909 a Studies on chromosomes. V. The chromosomes of Meta- 



podius, etc. Jour. Exp. Zool., vol. 6. 



1909 b Differences in the chromosome-groups of closely related species 



and varieties, etc. Proc. Seventh Internat. Zool. Congr. 



1911 Studies on chromosomes. VII. A review of the chromosomes of 

 Nezara, with some more general considerations. Jour. Morph., vol. 22. 



1912 Studies on chromosomes. VIII. Observations on the maturation- 

 phenomena in certain Hemiptera, etc. Jour. Exp. Zool., vol. 13. 



PLATE 16 



EXPLANATION OF FIGURES 



Notonecta undulata 

 X2250 



1-2 Metaphase of first division, polar view, showing 14 chromosomes, two small 

 ones in center. 



S A, B Serial sections of spindle in side view, early anaphase, first division. 



A A, B, C Same, two central pairs arranged linearly. 



5 A, B, C Serial sections of spindle in side view, initial anaphase, second divi- 

 sion, showing 13 chromosomes, XY in center. 



6-7 Metaphase of second division, polar view. * 



8-9 X and Y on separate fibers. 



10 A, B Same in complete spindle. 



11 X and Y connected by oblique fiber. 



12 A, B Sister anaphase groups of second division, from same spindle. 

 13-14 Spermatogonial groups showing 26 chromosomes. 



* All the figures (except fig. 113) were drawn with the camera lucida. In some 

 cases, for the sake of clearness, overlying chromosomes have been displaced. 



