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MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



from its shaft. The tunnel is round in cross section, and is a rule the shaft is near its center. 

 A section of the organ through the middle of its shaft therefore is flask-shaped, the neck (shaft) 

 being 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 fissure between the lamellae. I have not observed any 



special nerves going to these 

 organs, but as they lie close 

 to the large nerves of the 

 lamella? better material may 

 reveal the innervation. 



There seems to me to be 

 but little doubt that these cavi- 

 ties are sensory organs of a 

 simple type, and but little 

 more doubt that their func- 

 tion is olfactory as was as- 

 sumed by Owen and others for 

 for the group of lamella? as a 

 whole. I find, however, no 

 .sensory structures upon the 

 lamella?, nor any indication of 

 these latter possessing any spe- 

 cial sensory function. 



The sensory organs situ- 

 ated between the outer three 

 or four lamella? may be less 

 developed than those between 

 the inner lamellae. 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 bases of the lamella? 

 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 undivided portions. A rather 

 complicated system of muscles extends from its base to the surrounding regions of the cephalic 

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



The inner side of the cephalic sheath and all the organs within it, labial lobes and buccal 

 cone, are covered with what may fairly be called a skin. This may easily be removed from their 

 surfaces, leaving the muscular bases of the organs bare. It consists of a single layer of columnar 

 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-fig. :f 



lamera lucida outline of a section of the lamellated 

 labial lobe of the female; x 13. 

 G, sensory pit. L, lamella; N, N, nerves of lamelhe. 



trgmi of the inferior 



