. The anatomy of Nautilus pompilius. Nautilus. 118 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. from its shaft. The tuinicl is round in cross section, and ms a rule the shaft is near its center. A section of the orj^an through the middle of its shaft therefore is flask-shaped, the neck (shaft) l)eing slightly bulged at its center. The shaft may, however, be at one end of the tunnel. Shaft and tunnel are lined throughout with a peculiar epithelium. The cells are extraordinarily slen- der, almost like threads in their proportions, and the free end of each is prolonged into a sensory spike, the m
. The anatomy of Nautilus pompilius. Nautilus. 118 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. from its shaft. The tuinicl is round in cross section, and ms a rule the shaft is near its center. A section of the orj^an through the middle of its shaft therefore is flask-shaped, the neck (shaft) l)eing slightly bulged at its center. The shaft may, however, be at one end of the tunnel. Shaft and tunnel are lined throughout with a peculiar epithelium. The cells are extraordinarily slen- der, almost like threads in their proportions, and the free end of each is prolonged into a sensory spike, the multitude of which causes the surface of the tunnel and shaft to appear ciliated. A very slender nucleus is situated in the basal third of each cell. None of the cells lining the cavity are glandular. The length of the cells varies greatly in different cavities, as well as in different regions of the same cavity. This peculiar epithelium may extend outward from the mouth of the shaft for a little distance into the ffssure between the lamellae. I have not any spe'ual nerves going to these organs, but as they lie close to the large nerves of the lamellfe better material may reveal the innervation. There seems to me to be Init little doubt that these cavi- ties are sensory organs of a simple tj'pe, and but little more doubt that their func- tion is olfactory as was as- sumed by Ow^EX and others for for the group of lamellae as a whole. I tind, however, no sensory structures upon the lamellie, nor any indication of these latter possessing anj' .spe- cial sensory function. The sensory organs situ- ated l)etween the outer three or four lamella^ may be less developed than those between the inner lamelhe. The shaft may be shorter; the tunnel short, or little more than a spherical pocket. In two cases the only indications of the sense organs were small hemispherical projections be- tween the ])ases of the lamellaj covered by the sensory epi- thelium. These were the two outer or
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