HYDATINADA. 13 
ventral side of the nervous ganglion in N. clavulatus, and on the dorsal side in 
N. brachionus ; but in other respects the nervous systems are alike; the side view 
(fig. 8a) of the female of the former showing precisely the same nerve-threads to a 
dorsal antenna which are exhibited by the male of the latter (fig. 1b). The ovaries in 
both species are flat horseshoe-shaped ribbons bearing a single row of germs. The 
chief points in which N. clavulatus differs from N. brachionus, besides those of the 
general shape, and of the size and position of the foot, are as follows. The gastric glands 
are long and cylindrical, and below them there are two pairs of short cca attached to 
the dorsal surface of the stomach. The stomach often appears as a long conical tube 
tapering to a cloaca above the foot, colourless when empty, or tinged above with a faint 
yellow tint when filling with food. Frequently, however, there is a deep constriction 
above its lower portion, thus forming an intestine ; and on one occasion I saw this con- 
striction suddenly disappear, and the contents of the intestine at the same time drawn 
up into the stomach. Mr. Gosse noticed that the body had its surface marked with 
minute oblong points, which were scarcely visible except at the edge. He observed 
also that the discharged egg was carried behind the cloaca, and that its development 
was extremely slow; no sensible maturation having appeared even several days after its- 
exclusion. The male is unknown. 
Length, ,), inch. Habitat. Hampstead (P.H.G.); Clifton (C.T.H.): not common. 
N. uypropus, Ehrenberg. 
(Pl. XV. fig. 2.) 
Yotommata hyptopus . 5 3 Ehrenberg, Die Infus. 1838, p. 426, Taf. 1. fig. 6. 
SP. CH. Corona without setigerous prominences; ciliary wreath single; foot 
about one-fifth of the total length, arising from the ventral surface and capable of being 
wholly withdrawn within it; trophi forcipate. Partially loricated. 
This must be a rare animal; for, since Ehrenberg found two specimens in 1835, no 
one but Dujardin and Perty records having seen it. I have myself only seen it twice ; 
but on one of these occasions I fortunately had many specimens, and so I was able to 
add something to Ehrenberg’s rather meagre details. ‘The first thing that strikes the 
observer is the creature’s odd, wabbling way of swimming. This is due, no doubt, to its 
unusual shape ; for it is greatly compressed, having a narrow dorsal surface, but a broad 
lateral one. The skin can hardly be termed a lorica, yet there are several places where 
it is much stiffened. The two curved edges down the dorsal surface (figs. 2, 2a), the 
undulating edge of the trunk beneath the neck, and the rim of the aperture into which 
the foot can be withdrawn, are all thick and unyielding. The corona is truncate, but 
bulges forward towards the centre. The marginal ciliary wreath is interrupted on each 
side by a long vibratile style. A grape-shaped mastax, with feeble forcipate trophi, lies 
close to the buccal orifice. Ehrenberg says that there is neither esophagus nor 
intestine ; and if his two specimens had their alimentary canals much distended with 
food, these organs would have appeared to be wanting. But in front of the true 
stomach, with thick cellular walls, there is a very thin transparent chamber (fig. 2a) 
often empty, and constantly puffed in and out, in ever-varying shapes. 
This, I think, is an @sophagus similar to those in Asplanchna and Syncheta; and, 
like them, capable of being distended with food, so as to be confluent with the stomach, 
or of collapsing to form a narrow tube. The apparent absence of intestine is also a 
temporary condition of the alimentary canal: my specimens had all a most well-marked 
intestine. The gastric glands are large and plainly nucleated; and the walls of the 
stomach are studded with unusually large oil-globules. The contractile vesicle is high 
on the ventral surface owing to the whole animal being tucked up, as it were, towards 
that surface. The lateral canals are unusually large and distinct; and lie, with their 
floccose ribbons, close to the skin: they are well shown in fig. 2b. The same figure 
