PUE-OCULAR AND POST-OCULAR TENTACLES OF NAUTILUS. 201 



to the identification of the post-anal papilla as a pair of 

 osphradia, as has been recently suggested.^ 



However^ by means of macroscopic sections of fresh material 

 the presence of vibratile cilia on the sensory epithelium of both 

 the inner and outer osphradia can be demonstrated, and this I 

 regard as the final proof of the osphradial character of the 

 so-called post-anal papilla (figs. 4, 5). The sensory epithelium 

 of both osphradia is distinguished from the surrounding ecto- 

 derm both by the presence of the cilia and by the general 

 absence of goblet-cells. 



The olfactory lamellae of the accessory olfactory tentacles 

 and the sensory epithelium of the osphradia are the only 

 places where I have observed vibrating cilia in Nautilus 

 hitherto. 



EXPLANATION OF PLATE 10, 



Illustrating Dr. Arthur Willey's paper on " The Pre-ocular and 

 Post-ocular Tentacles and Osphradia of Nautilus." 



Fig. 1. — View from above of the "hood" and tentacles of Nautilus 

 during life. 



Fig. 2. — To show the ciliated ridge of the olfactory tentacles. 

 Fig. 3. — To show the suctorial ridges of the ordinary tentacles. 



Fig. 4. — The ciliated structure of the surface of one of the anterior 

 osphradia. 



Fig. 5. — Ditto of the posterior. 



Fig. 6. — Outline sketch of the Gastropod Aplustrum to show "laminate 

 organ " comparable to the olfactory tentacles of Nautilus. 



' W. Garstang, " The Morphology of the MoUusca," in ' Science Pro- 

 gress,' vol. V, March, 1896. 



VOL. 40, PART 1. — NEW SER. 



