144 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



papilla 1 , calling them osphradia, and suggesting that they correspond to the osphradia found so 

 widely distributed among- the Mollusca. Their specimens were not sufficiently well preserved to 

 allow an histological examination of the papillae, so the hypothesis depended entirely upon the 

 evidence of their innervation. Lankester and Bourne describe a small nerve as arising from 

 the nerve to the anterior gill near the fork of the branchial nerve and running into the papilla. 

 This innervation corresponds to the innervation of the osphradia of other Mollusca. 



Willey (1895) describes a small nerve proceeding to the osphradium of Lankestek and 

 Bourne from the point of bifurcation of the branchial nerve. He also suggests that the 

 preanal papillae represent a pair of osphradia, "corresponding metamerically with the pair 

 described by Lankester and Bourne between the bases of the gill plumes." This suggestion is 

 based upon the form, and variations in form, and upon the innervation of the papillae. It has 

 already been stated that the halves of the preanal ridge may be entirety separated, and that they 

 are always distinctly marked. 



Willey finds that a small nerve arises beside (inside of) each visceral nerve and runs back- 

 ward close to it. Arriving at the point at which the visceral nerves bend outward, the inner 

 nerves continue near the median line, passing into the mantle; they were traced through the 

 nidamental gland of the female. In regard to the relation of this nerve to the preanal papilla 

 Willey says: "The inner and smaller visceral nerve passes over the region of the renal sacs on 

 each side to the base of what I may call the posterior osphradia, to which it undoubtedly sends 

 nerve fibres, although I can not say positively that I have definitely traced these.'' 



In another place in the same article he says: "As to the innervation, I will say at once that 

 it is very difficult to see the actual nerves or nerve fibres (because the nerves are often not 

 compact trunks, but broken up into loose strands) which pass into the osphradia; but the anatom- 

 ical relations of the visceral nerves to the osphradia, which, I think, have never been fully 

 described, are such as to leave no doubt as to the source from which the osphradia derive their 

 innervation.'" 



Willey called attention to the fact that these two papilla? have essentially the same topo- 

 graphical relations to the anterior gills which the osphradia of Lankester and Bourne have to 

 the posterior gills. '•Their greater proximity to the middle line is shared in common with the 

 posterior (anterior) renal sacs and apertures and even the posterior (anterior) branchial veins, 

 as compared with the corresponding anterior (posterior) structures. That they are bifid, and 

 therefore more highly developed than the anterior (posterior) osphradia, is in keeping with 

 their position in the living Nautilus in the anterior region of the mantle cavity, and also with 

 the fact that the posterior (anterior) branchiae, with which they would be associated in the 

 metameric system, are considerably larger than the anterior (posterior) branchiae." The words 

 in parentheses indicate the relative natural position of the organs, Willey having described 

 them as they appear after the mantle has been turned back. 



Willey 1 s argument for the metameric relation of the anterior gills and the preanal papillae 

 appears to be strengthened by the fact that in the young specimen already mentioned he found 

 the gills closely approximated in the middle line, and in that case the preanal papilla? could 

 not have been far from the bases of the anterior gills. 



In a later article Willey gives more interesting facts in regard to the structure of the 

 osphradia. "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 osphradia! character of the so-called postanal papillae. The 

 sensory epithelium of both osphradia is distinguished from the surrounding ectoderm both by 

 the presence of the cilia and by the general absence of goblet cells. 



'"The olfactory lamellae of the accessory olfactory tentacles (the pre- and post oculars) and 

 the sensory epithelium of the osphradia are the oDly places where I have observed vibrating cilia 

 in Nautilus hitherto." 



A set of serial sections of the preanal papilla? of a male brought to light an interesting 

 structure in this. In the baseof each papilla is a gland composed of a numberof irregular branching 

 tubules. (Fig. 69, G.) Each opens separately to the exterior through a very minute pore. The 



