610 Gro. W. TANNREUTHER, 
Introduction. 
The investigations in the following paper were undertaken for 
the purpose of studying the development of certain aphids. The 
significance attached to the development of aphids from different 
kinds of ova, — sexual and parthenogenetic, — which have the same 
origin, appearance and fate, the one requiring fertilization and the 
other not, can not be overestimated. The behavior of these eggs 
during maturation and the relation of the sexual to the partheno- 
genetic individuals, afford invaluable material in attempting the 
determination of sex. 
With the importance of these facts in view, I propose to give 
the history of the aphids upon which the results of this paper are 
based, paying special attention to the phenomenon of spermatogenesis, 
ovogenesis and early development. 
The work of most previous investigators concerned mostly the 
habits and life history of the aphids, only incidentally touching the 
problems of morphology and cytology of the germ cells. 
STSCHELKANOVZEW, J. P., 1904, was among the first of the in- 
vestigators to take up the cytological problem of the aphids. He 
studied the maturation of the parthenogenetic eggs in Aphis rosae 
and found fourteen chromosomes of various sizes in the prophase of 
the maturation spindle. After the formation of the polar body, the 
nucleus contained eight single and three double chromosomes. 
STEVENS, N. M., 1905, studied the germ cells of Aphis rosae and 
Aphis oenotherae. In the maturation of the parthenogenetic eggs of 
Aphis rosae, ten chromosomes of five different sizes were found. 
This being the somatic number no reduction took place in the 
formation of the single polar body. In the maturation of the sexual 
egg, five chromosomes, the reduced number, occurred and both 
maturation divisions were longitudinal. 
Natural history. 
The life history of the aphids was studied not only for the 
purpose of getting a clearer idea of the relation of the partheno- 
genetic and sexual generations as they occur in nature, but from 
an experimental standpoint. Individuals from each succeeding par- 
thenogenetic generation were sectioned and studied in order to 
determine if any morphological or cytological differences occured, 
