REPORT ON THE MY ZOSTOMID A. 
67 
to the disk, being sometimes turned towards it and sometimes away from it. The shape of 
the cysts, and their proportion to the parts of the arm is also quite different. Sometimes 
they are extended and sausage-shaped (fig. 2), sometimes more ovoid (fig. 1), sometimes 
(fig. 3) intermediate between these two forms ; the cysts are never longer than 3 mm., 
or broader than 2 mm. Some lie longitudinally in the ambulacra! furrow of the arm 
(fig. 2) ; some extend along the pinnule (fig. 3) ; some are independent, and only attached 
by one extremity (fig. 1), where the cyst is laid transversely over the arm and bent 
to the antambulacral side. One cyst arises from the ambulacral furrow, and becomes 
attached to two opposite pinnules growing along their bases. The great thickness of the 
wall of the cysts is shown in the section (fig. 4). Every cyst contains a large brown 
coloured female ( $ ) and a small yellowish dwarf male ( $ ). The latter is transparent, 
and lies with its ventral side close to the side of the cyst, and with the dorsal side turned 
towards the female. The female has its lateral parts bent up aud touching on the 
dorsal side, so that a tube is formed, the exterior wall of which is formed by the ventral 
surface, while the dorsal side forms a canal which is trilateral in section, and contains 
numerous eggs (fig. 4, x). As in Myzostoma injiator and Myzostoma murrayi, so in both 
sexes in the present species the suckers are absent ; the female has no parapodia, but in 
their place are traces of the hook-apparatus. In neither sex are there cirri ; the mouth (m.) 
and cloaca (cl.) are terminal. 
The most striking difference between this species and the other dioecious species is, 
that the female possesses rudiments of testicles besides the ovaries, which together occupy 
all the available space between the alimentary canal and the body- walls. The rudiments of 
the testis are in the form of collections of small cells ( t .), closely resembling the immature 
testicular follicles of hermaphrodite forms, situated beneath the intestine ; the existence 
of these rudiments is interesting, inasmuch as this species forms therefore a link between 
the hermaphrodite and dioecious Myzostomida. 
The intestinal ramifications of the female (i.) reach almost to the margin of the body, 
and between them pass bundles of muscular fibres running from the dorsal to the ventral 
surface. The female is very firmly attached to the walls of the cyst, so that it was found 
impossible to detach one without injury. It appears to be circular in form, with a 
diameter of 2 mm. at the outside, and considerable thickness. The female shown in 
fig. 4 was *6 mm. thick in the middle of the body, and '2 mm. at the commencement of 
the lateral portions of the body. 
The male (fig. 5) is smaller than usual. It is circular in form, with a diameter of *8 mm. 
The compact testicles (t.), with the marginally situated genital apertures ($), placed 
somewhat behind the middle of the body, and the intestinal canal (q-f 3 , the cseca; r, the 
small rectum), are distinctly visible, and though I was unable to follow the intestinal cseca 
to their extremities, it appears that they differ from those of the female in not reaching the 
margin, but leave a large marginal zone unoccupied. The parapodia (p.) are small, 
