Introduction to A nimal Morphology. 3 1 7 



the outer wreath being incomplete over the funnel, 

 and consisting of nineteen at each side, the two dorsal 

 of which unite to form a cucullus, which, when the 

 animal is retracted, acts as an operculum. The inner, 

 smaller circlet consists of twelve tentacles on each 

 side. Each of these tentacles has a basal sheath, and 

 in the male the sheaths of the four ventral inner ten- 

 tacles unite to form a spadix.* The female Nautilus 

 has ninety-six tentacles. f The genus has a double 

 musculus columellaris from the shell to the head car- 

 tilage, not continued into the tentacles. 



The other Cephalopods have eight arms in a 

 circlet round the head, formed of the modified margin 

 of the foot, and two longer tentacular arms arising 

 within these. These arms may be united by membrane 

 to their tip (Cirrhoteuthis), or only at their bases ; they 

 are numbered from their dorsal side as first, second, 

 third, and fourth pair. 



Each arm consists of a central canal, containing an artery, 

 a vein, and a nerve. Circular and longitudinal fibres sur- 

 round this, and a dermal layer over all. Its oral surface is 

 covered with rows of cup-like suckers, each of which has a 

 smooth or toothed, hard epidermal ring round its mouth. 

 Radial and papilla-forming vertical piston-fibres, by retract- 

 ing the centre, help it to act as a sucker or adhesive organ ; 

 sometimes (Onychoteuthis) some suckers are modified into 

 hooks. The m. columellaris in these is represented by a 

 muscle extending from the head-cartilage. There are also in 

 all Cephalopods — i, 7?i. collaris, a broad band around the 

 neck ; 2, depressor inftmdibuli ; and 3, adductor infundihuli, to 

 alter the position of the funnel ; 4, m. lateralis (under the 

 ganglion stellatum in ordinary cuttlefishes), passing from the 



* Somewhat similar to the hectocotyhzed ann of a Dibranch. 

 t 38 external, 24 internal, 14-15 pair of labial ten-tacles, and 2 pair 

 of tentacles behind the eye. The male has 66. 



