24 VAN DER HOEVEN ON THE ANIMAL 



two other slits, very near to each other, and at the outward side of them is a little 

 depressed papilla, afBxed to the posterior surface of the root of the first branchia. The 

 first and the last slits are the exterior openings of two lateral blind sacs, containing the 

 follicular appendages of the branchial arteries ; the second slit communicates with the 

 pericardium'. At the first slit I once found a calcareous reddish-white and friable con- 

 crement ; I believed it to contain uric acid, but the chemical inquiry of my friend 

 Professor Van der Boonchesch has not confirmed my supposition. 



Behind the anus there are on each side two small and depressed caruncles, very simi- 

 lar to that mammillary eminence or papilla we have seen at the root of the first branchia. 

 External to those caruncles and behind them is a series of small orifices, not unlike to 

 the openings of the Meybomian follicles on the human eyelids. These are the emunc- 

 tories of the glandular organ, for the secretion of the covering matter of the ova. 



The head still requires some further description. In order to give a more correct idea 

 of the mutual superposition of the numerous digitations and processes which exist in 

 the Nautilus, instead of the eight or ten arms of the dibranchiate Cephalopods, I have 

 represented them from the left side, in three comparative figures, so as they follow each 

 other from the exterior surface of the head to the interior covering of the mandible 

 (see figs. 5, 6 & 7j. 



In the first place (PL VIII. fig. 5), the mantle / being reflected, the hood (a), the 

 different digitations (c, c), and the funnel {d), are visible. The large pedunculated and 

 perforated eye (6) has two tentacles (ophthalmic tentacles, Owen), one before its anterior 

 margin, the other behind, which are however not distinctly seen without reclining the 

 surrounding parts, and bending the eye-peduncle^. Only a few tentacles are protruded 

 from their sheaths, and partly visible. I never saw them protruded to such an extent as 

 in M. Laurillard's figures. The number of these digitations seems not to be exactly the 

 same in all specimens. Instead of nineteen digitations on each side, as in Professor 

 Owen's specimen, I twice found only eighteen. M. Valenciennes found only seventeen in 

 his specimen. That the hood is formed according to the ingenious supposition of Pro- 

 fessor Owen, by two large digitations conjoined along the mesial line, has been mentioned 

 above. The hood indeed contains two tentacles, and in this manner the whole number 

 of exterior or digital tentacles varies from eighteen to twenty on each side. 



' The three pairs of openings have been first observed by Professor Valenciennes. This point of the anatomy 

 of the Nautilus has been chiefly elucidated by the observations of my friend Professor W. Vrolik (Tijdschrift 

 voor de natuurkundige Wetenschappen, uitgegeven door de Eerste Klasse van het Koninklijk-Nederlandsche 

 Instituut, ii. 184'9, p. 312-315). Professor Owen describes in his memoir but one of those openings, and it is 

 therefore questionable what opening he speaks of. It seems however to me to be the second, because Professor 

 Owen describes the mammillary eminence which is nearest to this slit, and chiefly because the author observes 

 that the orifice " conducts from the branchial cavity to the pericardium." (Memoir on the Nautilus, p. 27.) 



' Under the eye is a part, first noticed by Valenciennes, a little hollow caruncle, with bilabiated aperture, 

 which seems to be the true organ of smell (see fig. 8). It is only visible by bending the eye behind and above, 

 and adheres to the root of its stalk. 



