60 



Fig. 2. An ophthalmic tentacle magnified, showing its laminated structure. 



Fig. 3. A digitation with its tentacle, magnified. 



a. The free extremity of the digitation. 



a. The cut surface separated from the parietes of the head. 



b. The digital tentacle. 



h'. The cut-surface of the tentacle, exposing 



c. The central nerve. 



PLATE III. 



Fig. 1. The supine or upper surface of the head of Nautilus Pompilius. 



a. The origin of the mantle. 



b. The dorsal fold collapsed. 



c. The apex or anterior extremity of the hood. 



d. The concavity at the base of the hood, which is adapted to the involute 



convexity of the shell. 

 e. e. The posterior angles of the hood, drawn outwards to show their form. 



/. The middle superior surface of the hood. 

 g. g. The lateral surfaces. 



h. The groove which separates the hood from the digitations. 

 i. The semilunar ridge which supports (in the reversed position) the involute 

 convexity of the shell. 

 k. k. The papillose digitations, which appear to form part of the hood. 



Fig. 2. The prone or under surface of the head of Nautilus Pompilius, with the 

 mantle divided and the sides of the funnel divaricated to expose its cavity and 

 the shell-muscles. 



a. a. The divided portions of the mantle. 



b. b. The digitations. i 



c. c. The funnel. 



d. d. Its lateral processes. 

 e. Its valve. 



/. The external portion of the left crus or pillar of the funnel. 

 g. The external portion of the right pillar turned outwards to show 

 h. The compressing muscle. 



