256 Edmund B. Wilson: 
Hemiptera (Nezara hilaris, Oncopeltus fasciatus); but further 
study has proved (1910b, 1911) that in the case of Nezara I 
was mistaken, while in case of Oncopeltus I am not yet prepared 
to express a final opinion. 
In all of the foregoing cases the male is the digametic sex 
and the female is homogametic. Thus far but a single case of 
the reverse condition has cytologically been made known — that 
of the sea-urchins Sphaerechinus and Echinus, which have recently 
been carefully studied by Baltzer (1909). Here a study of 
the fertilization-stages shows that all the sperm-nuclei are alike, 
while the eggs are of two classes, one containing a characteristic 
chromosome ”F“ which is never present in the sperm-nuclei and 
is replaced in the other class of egg by a chromosome of ordinary 
type. Eggs containing ”F“ must produce females, since this 
chromosome is never present in the spermatozoa. The male is 
therefore homogametic, the female digametic; but as regards 
sex-production the result is the same as in the first case. 
Fılchia | Stınea Pe Homo Ascans _ 
Thyanla | Prionidus lispinosa| Syromasles| Lumbricote 
Differential | | } 9 | 
Division | 
E23 Hır Male ” Gem 
Meere j 0 Tu N 
| Division 
ıın Hhe Female I a 
FF ; E 
se 20 | 080 ZEN 
DRSEE 000\ (el FS (00.0 
Formate 000) |N20) 0899 2) | 
ee 4. 
The final eonfirmation of the foregoing conclusions is given 
by the important discoveries of Morgan (1909), von Baehr 
(1909) and Stevens (1909b) in the phylloxerans and aphids, 
where all the fertilized eggs produce females. These discoveries 
prove that in these animals functional spermatozoa are produced 
only from those spermatids which receive the X-chromosome, 
while the others are rudimentary and degenerate. Only the 
