554 



CEPHALOPODA. 



Fig. 235. 



liquely downwards and backwards, and if air 

 be blown or fluid injected through it, the large 

 cavity surrounding the anterior part of the eye- 

 ball will be distended, and the cornea ren- 

 dered convex. In the Poulp the corresponding 

 aperture (o,Jig. 216) is somewhat larger, and 

 situated more in the axis of vision : its inferior 

 and posterior margin is extended beneath the 

 opposite margin, so as to form a semi-transpa- 

 rent curtain behind the external opening. In 

 the common Calamary and the Onychoteuthis 

 the corneal perforation is still larger, vertically 

 oblong, and through it the capsule of the cry- 

 stalline lens, which projects through the scle- 

 rotic aperture, is immediately exposed to the 

 external medium. 



Organ of Hearing. This organ has hitherto 

 been found only in the Dibranchiate division 

 of the Cephalopods. It consists, as in the 

 Cyclostomous or lower organized cartilaginous 

 Fishes, of an acoustic vestibule, containing a 

 limpid fluid and a calcareous body or otolithe 

 suspended in a delicate sacculusto the filaments 

 of the auditory nerve, but without the semi- 

 circular canals, cochlea, or other parts which 

 progressively complicate the Organ of Hearing 

 in the higher animals. 



The vestibular cavities (a, 

 a,Jig. 235) are situated, not 

 at the sides, but at the base 

 of the cranium in that thick 

 and dense part of the carti- 

 lage which supports the sub- 

 cesophageal cerebral masses. 

 In the Cuttle-fish the cavities 

 are of a sub-quadrate form, 

 separated only by a thin septum (cj ; and they 

 are every where closed, except at the entrance of 

 the nerve. From their inner surfaces project 

 several obtuse moderately elongated processes 

 (b} b,fg. 235), of a soft elastic texture, which 

 support the central sacculus (d) and otolithe 

 (e), and doubtless serve to convey to it the 

 vibrations which affect the body generally. 

 The sinuosities in the intervals of these pro- 

 cesses seem to be the first rudiments of those 

 which in the higher classes are extended in the 

 form of canals and spiral chambers within the 

 substance of the dense nidus of the labyrinth. 

 The otolithe in the Sepia officinalis is of an ir- 

 regular flattened quadrangular figure, with two 

 of the angles produced so as somewhat to re- 

 semble the human incus : the surface next the 

 parietes of the sacculus is convex and smooth, 

 the opposite one concave and broken : it is 

 white and transparent. (In^zg.235, the oto- 

 lithe is seen as exposed in the sacculus on the 

 right side.) 



lu the Octopus vulgaris the vestibules are 

 nearly spherical, and their parietes are smooth ; 

 the otohthes are of an hemispherical figure at- 

 tached to the dorsal part of the membranous sac, 

 of a white colour on the adherent surface, and 

 yellow on the opposite side : the rest of the 

 sacculus is filled with a transparent gelatinous 

 fluid. The auditory nerve divides into three 

 branches, which spread over the sacculus, and 

 convey to the sensorium the vibrations which 

 affect the otolithe and its sac. 



Organ of Hearing, 

 Cuttle-fish. 



In the Eledone cirrosa the otolithe is shaped 

 like the shell of a limpet, with the apex rounded 

 and curved backwards ; of a pink colour on the 

 sides, but of a white semitransparent texture 

 internally. 



The otolithes in all the Dibranchiates effer- 

 vesce with acids, like other substances com- 

 posed of carbonate of lime ; and in the Poulp, 

 Eledone, and all the Decapods except the 

 Cuttle-fish, they are the only earthy substances 

 which enter into the organization of these 

 animals. 



Organ of Smell. The sense of smell has 

 been attributed to the Cephalopods by all natu- 

 ralists who have written on their habits ; from 

 Aristotle, who mentions the strong-scented 

 herbs which the Greek fishermen attached in 

 his day to their baits, in order to prevent their 

 being destroyed by the Mollia, down to 

 Cuvier, who expressly asserts that they are at- 

 tracted by the odour of different substances. 

 But no organ expressly appropriated to the ex- 

 ercise of the olfactory sense has been deter- 

 mined in the Dibranchiate Cephalopods. 



In dissecting the Nautilus Pompilius, our 

 attention was directed to a series of soft mem- 

 branous laminae (fi,fg. 231) compactly arran- 

 ged in a longitudinal direction, and forming a 

 circular body very closely resembling the lami- 

 nated olfactory organ in Fish. The position of 

 these laminae, as well as their form and arrange- 

 ment, supported the belief that they exercised 

 the functions of an olfactory organ; being 

 situated just before the entrance of the mouth, 

 between the internal labial processes : nerves 

 were also traced to them from the inferior labial 

 ganglions. From analogy we are inclined to 

 suppose that the external lips in the Dibranchi- 

 ate order may be the seat of the olfactory sense. 



Organ of Taste. From the elaborate struc- 

 ture which the tongue displays in both orders 

 of Cephalopods, there can be no doubt but that 

 these destructive creatures fully relish the prey 

 that they devour, and, in correspondence to their 

 particular tastes, are led to select those species 

 the limitation of whose increase is assigned to 

 their charge. 



The anterior soft papillose lobes of the 

 tongue of the Nautilus are shewn in the sub- 

 joined figure (jig- 236), in which they are 



Fig. 236. 



denoted by the letter c; e indicates the middle 

 spiny plate, f the posterior coarser papillose 

 surface, and g the faucial folds. The nerves 

 of this part are derived from the brain itself, or 

 supra-cesophageal mass. 



