280 MR. J. D, MACDONAI.D ON THE ANATOMY OF NAUTILUS UMBILICATUS 
Valenciennes traced three small nervous filaments into a cavity of the cephalic 
cartilage, which he says was filled with a homogeneous pulp, and did not contain 
any kind of concretions; but not having had the opportunity of perusing his 
original memoir on the N. Pompilius, in which animal he observed this structure, 
I cannot determine with any degree of certainty the parts to which he refers. From 
my own observation, I can scarcely imagine that the nature of the venous sinus, 
which excavates the cephalic cartilage on either side, could be mistaken by a well- 
informed anatomist, and yet there is much probability in the suggestion of Pro- 
fessor Owen, that this is the locality to which Valenciennes assigns the organ of 
hearing. 
As our knowledge of the Mollusca advances, the localization of the special centre 
of audition, as well as the nature of the contents of the simple capsules, which shadow 
forth the vestibule of the more perfect apparatus of hearing, will prove of great im- 
portance to the natural classification of these animals. Thus, even with respect to 
the contents of the capsules, we find spherical otolithes present in the Heteropoda, 
Pectinibranchiata and several other orders ; and otokonia in the Pulmonifera, and as 
far as I have been able to discover, except while yet in their embryonic state, in the 
whole of the Pteropoda, including Peron’s PhylUrhoe, which is more closely allied to 
these last than to the Gasteropoda. Now as we know that the ear-chambers in the 
dibranchiate Cephalopoda contain single otolithes of large proportional size, although 
this rule may not be general in its application, it would not be unreasonable to con- 
clude, from the evidence afforded by the Nautilus, that the auditory sacs of the ex- 
tinct Tetrabranchiata were distended with minute pulverulent otokonia. 
Organ of Taste . — Although a doubt may still exist as to the locality of the olfac- 
tory sense in the Nautilus, this can hardly be said of the organ of taste, the mucous 
membrane of the mouth is so richly supplied with sentient papillae. These bodies 
are distributed in three principal groups ; thus a considerable number beset a stout 
vertical fold of the lining membrane, extending, on either side, from the root of the 
tongue to the back of the pharynx. The papillae are more numerous on the inner 
side and along the free border of each fold, in order to give them a greater extent of 
motion and render them opposable to the remaining group (Plate XV. fig. 4 b), 
which occupies the median line, between the orifice of the tongue-sac, a, and the 
commencement of the oesophagus, e; and although placed a little posterior to the 
organ usually recognized as the tongue in the higher Mollusca, they may with great 
propriety be named the lingual papillae, to distinguish them from the others. All 
the papillae agree, however, in their general character and minute anatomy, being 
either simple or compound, exhibiting much irregularity in form, and being clothed 
with long and delicate columnar epithelial cells, the homogeneous basement mem- 
brane enveloping a kind of areolar tissue. 
Renal Organs . — It is reasonable to suppose that an animal possessing a complex 
digestive system for the reduction of crude animal matter, should be also furnished 
