o/ Nautilus Pompllius. 63 



length it is about 2 centimeters narrower in females. With this 

 also is connected a difference in the form of the shell : in male 

 specimens it is broader and rounder at the aperture, more com- 

 pressed laterally in females. The margin of the aperture of the 

 shell also is, as it seems to me, more decidedly sinuous in the 

 male, in the female more even. 



These differences are, however, of small moment in comparison 

 with that which the investigation of the slips situated more in- 

 ternally, and called by Owen processus labiales, presents. If we 

 divide in Nautilus, whatever be its sex, the thickness of the 

 hood raesially and then turn the external slips away from each 

 other on each side, we find that the smooth inner skin, which 

 covers the inside of the entire sheath, formed by these slips and 

 the hood, gives off a fold of skin to which membranous thicken- 

 ings are attached. These are divided into slips, which form 

 cases in which retractile tentacles, similar to the external but less 

 in size, are enclosed. Let us consider this disposition in the first 

 place in male individuals somewhat more closely. The dermal 

 fold, of which we have spoken, is here attached downwards with 

 a free margin to the inside of the external circle of tentacles ; the 

 margins of attachment of the left and right sides of the dermal 

 fold are distant from each other about 15 millimeters. Upwards 

 on this fold is seen a membranous thickening {labial process) of 

 about 3 centimeters in length, which at its anterior margin splits 

 into eight flat digitiform sheaths. Through each of these sheaths 

 there passes a ringed tentacle. The two uppermost slips are 

 short, placed low on the basal part of the laminiform thickening, 

 and are bent backwards ; the six remaining slips are placed higher 

 and are longer*. On the outside of this same dermal fold, but 

 still also arising from it, there lies downwards, on the right side, 

 a small membranous lobe which splits into four tentaculiferous 

 slips. On the left side, in the same position, but extending 

 farther backwards and more clearly distinct from the dermal 

 fold, is found a large and thick body which is formed by the union 

 of four largely developed and modified tentacles. We name this 

 body, to which we shall recur, the spadix. It is the most cha- 

 racteristic part of the male Nautilus. 



Besides these lobes and the tentacles contained in them, no 

 other organs are found within the ring of the large tentacle- 

 slips. The fold, so often spoken of, passes from above inwards 

 into the skin which covers circularly the membranous, large, 

 round, muscular mass surrounding the beak, and which, around 

 the apex of the jaws, terminates in many short and tortuous 



* The breadth on the left side amounts to 1, on the right side to 2 cen- 

 timeters. 



