he determination of
sex in insects. Science, vol. 22, no. 564.

'05_b_. Studies on chromosomes. II. The paired
microchromosomes, idiochromosomes, and heterotropic
chromosomes in Hemiptera. Journ. Exp. Zool., vol. 2, no. 4.

'06. Studies on chromosomes. III. The sexual differences of
the chromosome-groups in Hemiptera, with some considerations
of the determination and inheritance of sex. Ibid., vol. 3,
no. 1.

DESCRIPTION OF PLATES

[The figures were all drawn with Zeiss oil-immersion 2 mm., oc. 12, and
have been reduced one-third, giving a magnification of 1,000 diameters.]

PLATE VIII.

_Trirhabda virgata_ (_Family Chrysomelidae_).

FIG. 1. Equatorial plate from somatic tissues of a male pupa, 27 large
chromosomes, 1 small one.

2. Equatorial plate from an egg follicle, 28 large chromosomes.

3. Equatorial plate of spermatogonium, 27 large chromosomes, 1 small
one.

4. First spermatocyte, synizesis stage.

5. First spermatocyte, early spireme stage, showing unequal pair of
chromosomes.

6-7. First spermatocyte, later growth stages.

8. First spermatocyte, prophase.

9-12. First spermatocyte, metaphase.

13. First spermatocyte, equatorial plate.

14-15. First spermatocyte, anaphase, showing separation of the elements
of the unequal pair (_l_ and _s_).

16. First spermatocyte, daughter plates.

17. Second spermatocytes, equatorial plates.

18. Second spermatocytes, equatorial plates showing V-shaped
chromosomes.

19. Second spermatocyte, early anaphase, the small chromosome in
metakinesis.

_Trirhabda canadense._

20. Equatorial plate from egg follicle, 30 large chromosomes.

21. Equatorial plate of spermatogonium, 29 large chromosomes, 1 small
one.

22. First spermatocyte, growth stage showing the heterochromosome group.

23. Heterochromosome group. _p_ = plasmosome, _l_ = large
heterochromosome, _s_ = small heterochromosome.

24-27. First spermatocyte, metaphase.

28. First spermatocyte, equatorial plate.

29. First spermatocyte, equatorial plate, small member of the unequal
pair only present.

30. First spermatocyte, daughter plates.

31. Second spermatocytes, equatorial plates.

32-33. Second spermatocytes, prophase.

[Illustration: STEVENS PLATE VIII

N. M. S. del.

COLEOPTERA]

PLATE IX.

_Chelymortha argus_ (_Family Chrysomelidae_).

FIGS. 34-35. Equatorial plates from egg follicles, 11 equal pairs, no
s