The Germ Cells of Aphis. 329 



V. SUMMARY OF RESULTS. 



1. There is no reduction in the number of chromosomes in the 

 female parthenogenetic egg. 



2. The 10 chromosomes form 5 pairs of different form and size. 



3. The polar body, at first extruded from the egg, later becomes 

 sunken in the cytoplasm, but takes no part in the development of 

 the embryo. 



4. The early segmentations are nuclear only, cell walls coming 

 in at a later stage. 



5. The young embryo takes in yolk material (the secundare 

 Dotter) from the vitellaria, through a definite valvular opening in 

 the oviduct. 



6. In the maturation of male eggs only one polar body is given 

 off, and there is no reduction in the number of chromosomes. 



7. The offspring of one parthenogenetic female are either all 

 females or all males. 



8. The ovaries of the parthenogenetic and of the sexual 

 females may be originally identical in structure, as shown (i) by 

 the presence of both kinds of ovaries in the same individuals; (2) 

 by the degeneration of about half of the oocytes in the posterior 

 half of the ovary of the sexual female embryo. The significance 

 of the latter phenomenon is uncertain. 



9. The reduced number of chromosomes appears in the polar 

 spindles of the winter eggs, and both divisions are longitudmal. 



10. The somatic number of chromosomes appears in the sper- 

 matogonia. 



11. Reduction in the spermatocytes is effected by longitudinal 

 pairing of the chromosomes immediately before the first matura- 

 tion mitosis. 



12. The first maturation division probably separates paired 

 chromosomes and the second is a longitudinal division ot the 

 original univalent chromosomes. 



13. The delay in separation of one pair of chromosomes in the 

 first maturation division is probably due to a different linin con- 

 nection from the others, rather than to any physiological peculiarity. 



14. There is no "accessory chromosome" in the male germ- 

 cells of aphids. 



Bryn Mawr College, 

 Dec. 20, 1904. 



