of Nautilus Poiiij)ilius. 65 



right side, fourteen on the h3ft side*. Within these innermost 

 tentacuhferous slips, under the membranous mass of the mouth, 

 there lies a part formed of eighteen or seventeen folds, which Owen 

 considered to be the olfactory organ, but which, in my opinion, 

 ought to be regarded as a continuation of the circle of innermost 

 tentacles, which are here present in a rudimentary state. This 

 part rests upon the fine membranous leaflets of the commissure 

 of the preceding slips. 



Here then it is apparent that a sexual difference exists. This 

 difference, as to its nature, must be investigated more closely. 

 It may be supposed that in the male Nautilus, as in the female, 

 two pairs of labial processes are present. The first pair then 

 would seem in the male to be placed above and internally ^ and to 

 carry eight tentacles, whilst in the female it is placed above and 

 externally J and carries twelve tentacles ; the second pair would 

 seem to differ from the undermost processus labiates of the 

 female in the small number of only four tentacuhy and still more 

 in lying on the outside of the uppermost slips. 



It was thus that I conceived the difference at an earlier 

 period f. Closer investigation, however, produced a different 

 conception, which I think preferable. Both sets of slips then in 

 the male individual are attached to the same dermal fold, although 

 the undermost set lies on the outside of the fold. I think, there- 

 fore, that these two groups of tentacles in the male Nautilus 

 correspond to one pair alone of the labial slips of the female 

 Nautilus, and that they are developed at the expense of the 

 other pair. The commissure at the under side shows, that the 

 pair to which they correspond is that of the outermost labial 

 slips of the female Nautilus. In this way of conceiving the 

 matter, the number also of the tentacles in the two sexes cor- 

 responds (8 + 4 in the male, 12 in the female). 



The sexual difference may now be stated more clearly. The 

 external labial slips are separated into two divisions, of which the 

 undermost lies downwards and carries four tentacles. On the 

 left side, this group of four tentacles is developed to form the 

 spadix. The undermost or innermost labial slips appear to be 

 wanting in the male. As rudimentary processus interni or infe- 

 rioreSj those parts however may be perhaps regarded which com- 

 pose the organ at the innermost commissure, situated under the 

 tongue and the jaws. The projecting leaflets in that part corre- 



* In one specimen I found fourteen on the right side, thirteen on the left. 

 Owen gives to these slips, as well as to the external labial slips, twelve 

 tentacles ; Valenciennes gives thirteen to each side ; W. Vrolik, fourteen. 

 Thus it appears that individual variety exists here, hut that a greater 

 number than in the external labial slips is to be regarded as the rule. 



t Trans, of Zool. Soc. iv. I. pp. 26, 27. 

 Ann. ^ May. N, Hist. Ser. 1^. l^ol. xix. 5 



