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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 ob.served 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 organs of one side. But there was no gradual transition from this to the more complicated 

 and apparently more typical form of organ. 



The muscles of the tentacles pass into the labial lobe as in other cases already described, 

 interlacing here with the numerous intrinsic muscles. The inferior labial lobe is a strongly 

 muscular and evidently contractile organ in both its divided and inidivided portions. A rather 

 complicated system of nuiscles ext(>nds from its base to the surrounding regions of the cephalic 

 sheath, providing for the motion of the lobe in all directions. 



The inner sidi- of the cephalic sheath and all the organs within it, labial lobes and Iniccal 

 cone, are covered with what may fairly 1h> called a skin. This may easily be removed from tlicir 

 surfaces, leaving the muscular l)ases of the organs bare. It consists of a single layei- of colunmar 

 epithelial cells similar to those upon the outer surface of the cephalic sheath, resting upon a thick 

 connective tissue dermis. The dermis tissue is somewhat fibrous, but reminds one strongly of 



Text-fi*:. :^. — CiiiiKTa lucida outline of a section of the lamelliitcti 

 labial lube of the female; ■ 1:5. 

 G, yensory jiit. L, lamella: N, X, nerves of lamella-. 



irgan i»f the inferior 



