41 



study. The hypothesis that connects it with the power they possess of black- 

 ening the water around them must fall to the ground, as the Pearly Nautilus, 

 in which this disposition of the pigment equally exists, has no apparatus for 

 secreting and ejecting an inky fluid. 



With respect to the sense of hearing, I have not been able to detect a distinct 

 organ for that faculty in the Pearly Nautilus. The cartilage supporting the 

 suboesophageal nervous circle was examined, as far as considerations for the pre- 

 servation of an interesting part of this rare animal would allow, but did not 

 appear to contain any cavities or calcareous bodies resembUng those in the 

 Dibranchiate Cephalopods. 



It has been conjectured, that in the MoUusks the organ of smell is as generally 

 diffused as that of touch, and that the entire skin, which from its softness and 

 lubricity resembles a pituitary- membrane, is the seat also of this sense. But in 

 the present species, the character of the exposed integument is opposed to the 

 idea of its being adapted to such a function, and in this respect the Pearly 

 Nautilus differs considerably from the rest of the class. These considerations 

 strengthen an opinion I had been induced to form from a previous examination 

 of the part, — that there exists in this Mollusk a distinct organ of passive smell, 

 formed after the type of that organ in the inferior Vertebrata, and especially 

 in Fish. 



The part which appears to exercise the functions of that modification of the 

 sense of smeU which is enjoyed by aquatic animals, consists of a series of soft 

 membranous laminae [I. pi. 4 ; g. fig. 1. & fig. 2. pi. 7.), compactly arranged in 

 the longitudinal direction, and situated at the entry of the mouth, between the 

 internal labial processes. These laminae are twenty in number, and are from 

 one to two fines in breadth, and from four to five in length, but diminish in this 

 respect towards the sides. They are suppUed by nerves from the small ganglions 

 which are connected to the ventral extremities of the anterior suboesophageal 

 ganshons. 



Tlie tongue of the Pearly Nautilus would seem to give it greater pretensions 

 to a possession of the sense, of taste than the analogous part in many of the 

 vertebrate animals ; the anterior caruncles, at least, appear peculiarly adapted to 

 this facidty. They are supplied with two ner\-es, which come otF from the brain 

 or central commissure. 



