381 



appear as though provision had been made for the entrance of sono- 

 rous waves through a rudimentary external ear. 



There can be little doubt that the eye itself is a modified tentacular 

 sheath, so fashioned and endowed as to become the seat of the special 

 sense of vision ; but the subserviency of such a part to the faculty 

 of hearing is much more obviously seen in the subocular process just 

 noticed, which holds an intermediate position between the organ of 

 vision and the tentaculiferous sheaths protecting the proper organs of 

 touch. 



In a figure which accompanies this communication, the auditory 

 sac is exposed by an incision made in the groove between the funnel- 

 lobe and the base of the tentacular sheaths. The subocular process 

 is slit open to the bottom of its cavity, so as to show its termination 

 in close proximity to the ear-sac. The interior of the tube is lined 

 with a glandular membrane thrown into small folds, disposed longi- 

 tudinally, but the exterior of the process is quite smooth like the rest 

 of the integument. 



I have often had some little difficulty in detecting the otolithes or 

 otoconia, as the case may have been, in gasteropods long immersed 

 in spirits or other preservative fluids ; but in a specimen of N. Pom- 

 pilius, kept for many months in strong gin, although the soft parts 

 were far from being well preserved, I was enabled at the first attempt 

 to remove the contents of the auditory sacs, and the minute elliptical 

 otoconial particles, identical in character with those of N. macrom- 

 phalvu, were very distinctly seen under the microscope. 



In a former paper, I first noticed my discovery of simple auditory 

 capsules in, as I then supposed, the N. umbilicatus ; but I find that 

 I have incorrectly named my specimen, for on comparing the shell 

 with the drawings of the several existing Nautili given in Sowerby's 

 'Thesaurus Conchyliorum,' it agreed exactly with the figure of N. 

 macromphalus . I am indebted to my friend Mr. S. Stutchbury for 

 the perusal of the work referred to, and my error is sufficiently ac- 

 counted for by the scantiness of my own library. 



With reference to the action of the great lateral muscles of Nau- 

 tilus, the following ideas have suggested themselves to my mind. 



As though preparatory to the complete separation of the body of 

 the Cephalopod from the shell, which is usually present in the lower 

 genera, the fasciculi composing the lateral muscles in Nautilus do not 



2 G 2 



