98 
5. Sexual System. 
The ovaries, when fully developed (see PI. LXV—LXVII, fig. 1, o v). 
have the form of two very large oblong oval sacs occupying the greater part of 
the body-cavity behind the carapace, often even extending for some distance 
within the part covered by the latter. They are generally in immediate contact 
with each other above, whereas below they diverge, to allow the intestine to 
run between them (see PI. LXY, fig. 11). Each ovarial sac contains a somewhat 
variable number of ova, which are all of nearly the same size and development, 
and by mutual pressure assume a more or less polygonal form. In Diastylis 
I have found from 30 to 40 such ova in each sac; in Leucon their number is 
much smaller, sometimes only 7 ova being found in each ovary (see PI. LXVII, 
fig. 1, o v, fig. 2). The ova are of different colour in different genera, being 
of a fine rose hue in Diastylis, whereas in Lamprops and Pseudocuma they are 
dark green. They contain a more or less opaque granular yolk, in the centre 
of which the germinal vesicle is faintly to be traced, and they are enveloped by a 
very thin pellucid membrane (see fig. 3). The uniform development of the ova in the 
ovarial sacs seems to indicate that the true germinal stratum must occur in another 
place, and indeed in quite young specimens of Diastylis I have distinctly seen a small 
median part connecting the 2 sacs, and exhibiting in the middle a dense stratum 
of small nucleated cells (see fig. 4). I have failed to detect any oviduct leading 
outwards from the ovarial sacs, and indeed, I believe that no oviduct in reality 
exists, the ova, by the rupture of the thin enveloping membrane, being simply 
received into the body-cavity, where they undergo their development. It is true 
that a marsupial pouch is found; but its cavity is confluent with the body-cavity, 
the thin incubatory plates being formed by the splitting of the ventral wall of the 
body itself. In gravid females, it is easily seen that the embryos are not confined 
to the marsupial pouch, but are distributed throughout the w'hole body-cavity 
behind the carapace, even up to the region of the heart. The purpose of the 
so-called marsupial pouch is thus merely to afford the necessary increase of 
breeding-space for the successive growth of the embryos. The Cumacea are 
accordingly true viviparous animals, and it is very probable that the females 
become gravid only once in their life, and soon die off after the breed has been 
discharged. 
The testes (see PL LXVIII, fig. 1, t) are rather difficult to observe in 
the living animal, as they are comparatively small, of whitish colour, and lie in 
such close proximity to the intestine as easily to escape attention. By dissec¬ 
tion of fresh male specimens, they admit, however, of being isolated and studied 
