Unpaired Heterochromosome in Aphids lij 



phases. Early stages (Fig. 9) do not indicate any inequality. 

 Later stages (Fig. 10) show some inequaHty in the size of the two 

 cells, but the lagging chromosome still seems destined to divide. 

 Here again, however, one finds in the prophase of the second 

 division a double chromosome (Figs. 11 and 12) which can be 

 accounted for only by supposing that the lagging chromosome 

 finally pulls back into the larger cell and folds together. In this 

 species the chromosomes can be counted in a few second spermato- 

 cyte prophases and metaphases of the smaller cells, as degeneration 

 occurs mainly in the spermatid cysts. Figs. 12 and 13 show pro- 

 phases of the two kinds of second spermatocytes, Fig. 13 being a 

 Smaller cell lacking the double chromosome. Figs. 14 and 15 

 are the corresponding metaphases. 



Among my preparations of aphids collected from Solidago altis- 

 sima, is one, rather Hghtly stained with iron hasmatoxylin, which 

 shows one chromosome black while the others are gray, in the 

 first spermatocyte prophases and metaphases. In the prophase 

 stage (Fig. 16) which was mentioned in my '05 paper as a possible 

 synizesis stage (PI. IV, Fig. 34), the dark staining chromosome is 

 the isolated one, and in the metaphase (Figs. 17, 18 and 19) it is 

 single while the other five are double. There are no anaphases 

 in this preparation. The typical anaphases found on other slides 

 are shown in Figs. 20, 21 and 22, Fig. 22 indicating a shifting over 

 to one of the pair of second spermatocytes of the whole of the 

 lagging chromosome and of considerable additional cytoplasm. 

 The prophases of the second division in this species (Fig. 18) do 

 not show the heterochromosome {x) double, and the anaphases 

 look as though it was simply pulled out at right angles to its 

 original long axis (Figs. 20 and 21) and later (Fig. 22), the pulling 

 being relaxed at one end, was returning to its original form. 

 Figs. 24 and 25 are second spermatocytes in metaphase, show- 

 ing five and six chromosomes, Fig. 25 being one of the very few 

 cases where it was possible to count the chromosomes in the 

 smaller cells. 



In the reddish brown aphid from the beach goldenrod, there 

 are anaphases of the first division in which the lagging chromo- 

 some is distinctly divided as in Fig. 26, others where it is wholly 



