85
AN ANDROGYNOUS DAPHNIA PULEX FROM
WARLEY.
By D. J. SCOURFIELD, I.S.O., F.L.S., F.R.M.S.
(With One Plate)
IN a Presidential Address to this Society,1 I called attention,
inter alia, to the occasional occurrence of individuals of
Entomostraca combining in various degrees the characters of
both sexes. At that time I had not myself seen such a case,
but more recently I have been fortunate enough to find two of
these androgynous, or gynandromorphic, specimens, both
belonging to the genus Daphnia. One of these occurred among
some specimens of a form of D. carinata hatched out from dried
material brought home by the recent Lake Titicaca expedition
and the other among the descendants of specimens of D. pulex
from a pond at Little Warley. As the occurrence of such
individuals appears to be very rare it is proposed in the present
note to put on record some particulars concerning the Essex
specimen.
The general appearance of the animal can be seen from
Figs. 1 and 2, which show in outline the right and left sides
respectively. If these are compared with Figs. 3 and 4, which
show respectively the heads of a normal male and female of the
typical form of D. pulex, to which form the specimen evidently
belonged, it will be seen that the androgynous specimen re-
produces male and female characters in a curiously mixed
fashion.
The almost straight ventral margin of the head is typically
male, as is also the presence of a fringe of "bottle-brush" setae
on the anterior ventral margins of both valves of the shell
On the other hand, while the enlarged and movable antennule
on the right side is almost typically male, except that it points
backwards instead of straight out (compare Figs. 1 and 3),
the minute and rigid antennule on the left side is essentially
female (compare Figs. 5 and 6). That it apparently arises
directly from the rostrum, instead of a little way back, is no
doubt only due to the male rather than the female form of
the front of the head.
1 Essex Naturalist, 1932, pp. 2-18.