HYDATINAD^E. 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. Ib). 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 casca 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, 5 J 5 inch. Habitat. Hampstead (P.H.G.) ; Clifton (C.T.H.) : not common. 



N. HYPTOPUS, Ehrenberg. 



(PL XV. fig. 2.) 

 Notommata hyptopus . . . Ehrenberg, Die In/us. 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 wholly withdrawn within it; trophi/o rcipate. 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 oesophagus 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 oesophagus similar to those in Asplanchna and Synchceta ; 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. 26. The same figure 



