THE CEPHALOPODA 



299 



inner base of the crown of arms : one such buccal pouch occurs in 

 Loligo and two in Sepia, and they may play an accessory part in 

 fecundation. In some exotic species of Sepia there are pouches in 

 the mantle. 



II. ANATOMY. 



1. The Alimentary Canal The digestive tube of Cephalopoda 

 comprises a buccal mass with two mandibles and a radula, a long 

 oesophagus, a muscular stomach with a pyloric caecum, and a short 

 intestine which turns forward and opens in the middle line below 

 the funnel (Fig. 252, ft). 



The buccal aperture, situated in the middle of the pedal 

 appendages (Fig. 260, w), is surrounded by a circular lip garnished 



with papillae. Further- 

 more, in the decapodous 

 Dibranchia there is a 

 buccal membrane which 

 may be very extensive 



Fio. '265. 



Minute structure of the cartilage of Loligo. 

 a, simple, and b, dividing cells ; c, canaliculi ; d, 

 an empty cartilage capsule, with its pores ; e, 

 canaliculi in section. (From Lankester, after 

 Ftirbringer.) 



Fio. 266. 



Mandibles of Nautilus, 

 in situ, dorsal aspect. 

 l.m, lower or ventral 

 mandible ; u.m, upper or 

 dorsal mandible. (After 

 Owen.) 



and be divided into lobes alternating with the arms, and the lobes 

 may even be furnished with small suckers, as may be seen in some 

 species of Loligo. 



The buccal cavity or pharynx has very thick muscular walls. 

 Internally it is provided with two powerful mandibles, one ventral 

 and the other dorsal (Fig. 266) ; the tip of the ventral mandible 

 overhangs that of the dorsal, forming a beak like that of a parrot 

 (Fig. 268, ?>m, dm). These mandibles have recurved insertion-plate*, 

 to which the large muscles forming the greater part of the mass of the 

 buccal bulb are nttached. In Nautilus the trenchant borders of the 

 mandibles are covered by a calcareous deposit (Fig. 266), and the 

 fossils known by the name of Rhynclwliths are nothing else than 

 the beaks of Tetrabranchia ; for instance, Rhyncholitlies hirundo is the 

 beak of Temnocheilas bidorsatus, of the Trias. 



