512 Katharine Foot and E. C. StrobeU, The Chromosonies of Euschistus etc. 
Photos 16 — 23. The First Generation of Hybrids (F^) from 
E. variolarius Q x E. servus d. 
Photos 16 and 17. Late prophase chromosomes of the first spermatoeyte mitosis. 
In both photographs the X Y chromosomes are clearly differentiated from the auto- 
somes. Both X and Y are preparing to dhdde as individuals while the autosomes 
are prepared to divide as bivalents. 
Photos 18 — 23. Metaphase chromosomes of the second spermatoeyte mitosis. 
In each of the six groups the X Y chromosomes are easily identified and show the tj-pical 
featimes of both parents. 
Photos 24 — 31. The second Generation of Hybrids (F^). 
Photo 24. Prophase chromosomes of the first spermatocjde mitosis. The X Y 
chromosomes are alniost in contact on the lower periphery of the group. Their method 
of division is clearly indicated, each preparing to divide indiA*idually. On the upper 
peripher}’ of the group one of the autosomes appears as a cross — a form sometines 
seen in both variolarius and serms. 
Photos 25 — 27. Late prophase or metaphase chromosomes of the first sperma- 
toc}’te mitosis. In photo 25 the X Y chromosomes are widely separated, the Y chromo- 
some being on the lower periphery of the group and the X chromosome on the right 
periphery. On the left periphery the two halves of one of the autosomes are far 
apart, probably due to the technique. In photo 26 the X Y chromosomes are sharply 
differentiated from the autosomes, the X chromosome indicating clearly a longitudinal 
division. The two halves of one of the autosomes are far apart. The relative size of 
the X chromosome to the autosomes shows an irregidarity which is sometimes seen 
both in variolarius and servus. In photo 27 the XY chromosomes are almost in 
contact on the lower periphery of the group. On the upper left periphery the two 
halves of one of the autosomes are apart. 
Photo 28. Telophase of the first spermatoeyte mitosis. In the center of each 
group is one half of the Y chromosome, a clear demonstration of its division in the first 
mitosis. The halves of the X chromosomes can be identified as the smallest in the 
circle of chromosomes. All the autosomes appear as dyads. 
Photos 29 and 30. Metaphase chromosomes of the second spermatoc}’te mitosis. 
In each of the two groups the X Y chromosomes are in contact and can be clearly recogni- 
zed by their inequality in size. 
Photo 31. Telophase of the second spermatoeyte mitosis. The chromosome 
groups of the two spermatids show the X chromosome in the center of the right group 
and the Y chromosome in the center of the left group. Compare these spermatids 
with those of variolarius in photo 9. 
