PLATE XXI 



i. Oral aspect of a Cephalopod {Loligo vulgaris, Lamk.). The mandi- 

 bles are seen in the centre surrounded by the circular lip, by the 

 buccal membrane (with two rows of small suckers on its lobes), by 

 the eight sessile arms (dorsal ones marked d) ; whilst the two prehensi'e 

 arms (t), with their enlarged extremities (e) armed with suckers, lie on 

 either side ventrally, and the position of the funnel behind is marked/. 



2. Oral aspect of Nautilus, expanded (after Loven) : h., hood ; s., 

 siphon or funnel. 



3. Diagrammatic sketch of the structure of a Cephalopod : cr., crop ; 

 /., funnel ; g., gill ; giz., gizzard ; i., ink sac ; m., mouth ; m.c] mantle 

 cavity ; 1-5, arms. The arrows show the direction of the current of 

 water in and out of the mantle cavity. 



4. Agonauta argo, Linn. Female swimming from right to left. 



5. Septal suture of an Ammonite (Arcestes bicarinatus, Munst.), show- 

 ing extremely complicated foldings. 



%* Fig. 3 drawn by Miss G. M. Woodward. The others from drawings by 

 S. P. Woodward. 



