4 STUDIES ON THE GERM CEIXS OF APHIDS. 



penetrating power, and because aphids will not sink in any water 

 mixture; but by opening the insects with needles in the fluid any 

 method of fixation may be used. 



Material from different species, though fixed in the same way, takes 

 the stain so differently that it has often been found necessary to 

 restain several times to get just the right differentiation for counting 

 and drawing the chromosomes accurately. Schneider's aceto-carmine 

 proved to be useful in determining the character of new male material. 



RESULTS OF INVESTIGATION. 

 The Rose Aphids. 



On the roses of this section, both out of doors and in the green- 

 house, one commonly finds a brown and a green aphid ; and on the 

 various hardy roses there appear in autumn winged mothers of another 

 species with large broods of white or yellowish winter-egg layers, and 

 a little later the winged males are present. The host from which this 

 latter species migrates to the rose for sexual reproduction has not yet 

 been discovered, and the parthenogenetic forms have, therefore, not 

 been studied ; it is, however, hoped that these may be obtained in the 

 spring from eggs laid on isolated rose plants in the greenhouse. 



In my last year's paper (Stevens, '05) the behavior of the female 

 germ cells, both parthenogenetic and sexual, of the brown rose aphid 

 was quite fully described ('05, pis. i-ui, figs. 1-27), but males were not 

 found. This year some males were obtained, but they were very few 

 compared with the number of sexual females, and for some reason 

 the material did not fix so well as that from most of the other species. 

 A few good drawings of the first spermatocyte were made from aceto- 

 carmine preparations of the testes taken from specimens collected 

 on November 13 (pi. I, figs. 13). The metaphase of the second 

 spermatocyte, from a section, is shown in figure 4. Figure 5, the 

 metaphase of a segmentation spindle, and figure 6, the maturation 

 mitosis of the parthenogenetic egg, confirm the results recorded in my 

 earlier paper, showing the double series of maternal and paternal 

 chromosomes in the parthenogenetic generation. No favorable mat- 

 uration stages of the winter eggs were obtained. The scarcity of 

 males was accounted for by the discovery of male and female embryos 

 in the same individual, but only one or two males to many females. 

 In this species the parthenogenetic females and the males are a reddish 

 brown, while the sexual females are red and the eggs when first laid 

 are green. The males are winged, the sexual females and the mothers 

 of the sexual generations apterous. 



