46 Royal Society : — 



blood passing through the brancliire under changes of pressure to 

 which the animal may be subjected at different depths. These fol- 

 licles are subcylindrical in form, and somewhat dilated at the free 

 extremity, to which is appended a folded and funnel-shaped process 

 of membrane which expands rather suddenly and presents a jagged 

 border. They open by an oval or slit-like orifice into the afferent 

 branchial vessels, on each of which, as Professor Owen has observed, 

 they are disposed in three clusters. The outer membi'ane is smooth 

 and glossy, homogeneous in structure, and sprinkled over with mi- 

 nute, rounded, transparent bodies, resembling the nuclei of cells. 

 Beneath this layer, flat bundles of fibres, apparently muscular, are 

 traceable here and there, principally disposed in a longitudinal direc- 

 tion, and sometimes branched. The lining membrane consists of a 

 loose epithelial pavement, similar in many respects to that of the 

 uriniferous tubules of the higher animals, the cells containing, be- 

 sides the nuclei, numerous minute oil-globules, or a substance much 

 resembling concrete fatty matter. This membrane is thrown up 

 into very numerous papillre and corrugations, so as greatly to in- 

 crease the extent of surface. The papilltB are more numerous to- 

 wards the attached end, and a circlet of longitudinal folds, with 

 transverse zigzag corrugations, radiate from the bottom of the fol- 

 licle, in which a number of small pits or fenestrations are sometimes 

 visible. The funnel-shaped membranous process above noticed is 

 continuous with the lining membrane. The cavity of each follicle, 

 therefore, communicates with the exterior through the centre of this 

 process, and the aperture is thus guarded by a kind of circular valve 

 permitting the escape of secreted matters, but effectually preventing 

 the entrance of fluid from without. 



Some considerations are next offered in support of the view 

 adopted as to the functions of these vascular appendages. 



Lastly, on the question whether the peculiarities of structure re- 

 cognized respectively in N. Pompilius and N. vmbilicatiis are suffi- 

 cient to establish a difference of species, or are attributable merely to 

 variety, the author observes, that any tendency in a being to revert 

 to an original type, when such has been determined, betrays variety; 

 but this tendency is never manifested in the Nautili under consider- 

 ation by the occasional occurrence of specimens presenting charac- 

 ters which place them intermediately between N. Pompilius and 

 N. umbilicaius . Having visited the Fijii Islands since he formerly 

 wrote on N. Pompilius, he finds that the umbilicated Nautili are not 

 known to the natives, although N. Pompilius is very plentiful ; but at 

 Fatuna or Wallis's Island, where both are found, the people recog- 

 nize the dift'erence between them depending on the presence or 

 absence of umbilical pits. On this the author remarks, that although 

 particular localities, with all attending circumstances, may favour 

 the production of varieties, yet the permanence of the distinctive 

 characters of these Nautili without symptom of amalgamation, and 

 the discovery of a female specimen of N. umbilicatus, are strong 

 arguments in support of the view that they are distinct species, 

 though very closely allied. 



