Sex Determination in Phylloxerans and Aphids 303 
In 1907 Tannreuther published an account of the germ cells of an 
aphid, Melanoxanthus salicis. He has confused the sequence of 
the stages to such an extent, and has overlooked so many of the 
essential facts, that a detailed criticism of his statements would be 
unprofitable. I suspect furthermore that his account of intranu- 
clear polar body formation is entirely erroneous. 
Another species of aphid, Lachnus dentatus, gives rise to sexual 
forms late in the autumn. Itcontainsalarge accessory and another 
s) er a) 
c 
jo ©® 
E 
Os 
(Je 
e H ‘ J 
Fig. XXII Lachnus dentatus. 4-D, F, second spermatocyte, equatorial plates; E, F (lower 
half), rudimentary cells; G, part of ovary showing rudimentary cells (black); H-7, second spermatocyte 
divisoin. 
very small chromosome, besides two others in the reduced number. 
L was not without hope that this might prove an analogous case to 
that of Phylloxera caryecaulis and that the smallest chromosome 
might be a small accessory in addition to the large one. This is; 
however, not the case as the following facts show. 
Equatorial plates of the first spermatocyte division are drawn in 
Fig. XXI, B-I; side views of the dividing plate in Fig. XXL 
L-P; and later stages in Fig. XXI, Q-X; Fig. XXII, F. In Fig. 
XX, K—P, the division of the smallest chromosomes is clearly seen. 
The unequal division of the cell is shown in Fig. XXI, R-W. 
