86 THE ESSEX NATURALIST.
In addition to the foregoing characters, one or two others,
not shown in the figures, may be referred to. The first foot on
the right side, although without the large hook characteristic
of the male, was nevertheless somewhat different from that of the
female and was provided with the very long flagellum of the
male. The left first foot, however, appeared to be entirely
female. The post-abdomen was somewhat intermediate in
outline between the male and female form of that part, being
more bayed on the dorsal edge than in the normal female,
though less so than in the male of the typical form of D. pulex.
The four abdominal processes were just as in the ordinary
female and did not show the suppression of the first (anterior)
and elongation of the second which is so characteristic of the
same typical form of D. pulex. The sexual organs on both sides
appeared to be true ovaries showing incipient production of
ova and reserve food material. No trace of sperm could be
made out.
From the foregoing description it is evident that the specimen
was mainly female in character, and this was supported by the
fact that, just before Figs. 1 and 2 were drawn, it had produced
and thrown off an ephippium (i.e. the modified part of the back
of the shell destined to receive the sexual eggs), although no
eggs had been deposited therein. Nevertheless the tendency
towards the production of male characters was very strong,
though more so on the right than on the left side, thus showing
the asymmetrical development so often seen among androgynous
individuals.
It may be mentioned here that the peculiar bump on the
dorsal margin and the but slightly curved and smooth character
of the latter indicate that the specimen was in the post-ephippial
condition when drawn. Prior to the production of the
ephippium the back was rounded as in ordinary parthenogenetic
females, which probably means that parthenogenetic eggs had
previously been produced, although these had not been observed.
It must not be thought that androgynous individuals,
which occur sporadically in many groups of animals, are merely
interesting curiosities of no particular importance from the
point of view of general biology. On the contrary they raise
intriguing questions in connection with the determination of
sex and the mechanism of growth and development.