98 



5. Sexual System. 



The oraricSj 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. LXV, 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 Diatiti/liv 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 hody-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 whole 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 tcstcs (see PI. 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 



