ON THE ANATOMY OF NAUTILUS POMPILIUS. 211 



12. A prolongation backwards of the nerve-trunk which 

 supplies the gills probably represents the postanal commissure 

 of Amphineura. 



13. A laminated organ lying below the mouth has a func- 

 tion in connection with copulation— the spermatophore of the 

 male becoming attached to it. 



14. The evidence as to the "pedal" nature of the Cephalo- 

 pod arms appears to rest on insecure foundations, and it seems 

 desirable to abandon it for the inherently much more probable 

 view that these structures are processes of the head region. 



15. Nautilus shows many strong resemblances to the 

 Amphineura, and it is probably amongst these latter that we 

 have to look for the nearest allies of the Cephalopoda. 



EXPLANATION OF THE PLATES. 

 Plate IX. 



Fig. 1. Side view of an animal of Nautilus pompilius, extracted from the 

 shell. The funnel has been opened out and the mantle-flap partly- 

 cut away so as to give a better view of the various parts. 



h, hood; t, tentacles; e, eye ; /, funnel separated by a deep groove 

 from the hood-ten tacle mass ; m, cut edge of mantle-flap ; g, gill ; 

 s, siphuncle. 

 Fig. 2. Longitudinal section through the animal of Nawtilus very slightly 

 to the right of the middle line. 



6, buccal cavity; r, radula; eg, supra-cesophageal nerve-cord; 

 pl.g, posterior suboesophageal nerve-cord; p.g, anterior ditto; 

 /, funnel with its valve; ph, crop; int, intestine; an, anus; k, 

 kidney-chamber with follicular appendages of advehent vein pro- 

 jecting into it; p.foll, pericardial gland-follicles projecting into 

 pericardium ; v.c, vena cava. 



