374 



ORGANS OF DIGESTION. 



horny teeth, as in several of the gasteropods. The simple 

 unarmed mouth of the hyalea (Fig. 122. A. a.) leads into 

 FIG. 122. a narrow length- 



ened oesophagus 

 which passes un- 

 der a broad cere- 

 bral ganglion(l 22 

 A. y.) y and di- 

 lates in the ab- 

 dominal cavity 

 into a mem- 

 branous crop 

 (1 22. A. b.) which 

 is slightly mark- 

 ed internally 

 with longitudinal 

 plicae. This first 

 cavity opens di- 

 rectly into a short cylindrical muscular gizzard (122. A. c.) 

 likewise marked with longitudinal folds on its inner sur- 

 face, and lying, like the crop, over the great retractor 

 muscle (122. A. h.} by which the animal withdraws its 

 head and fins (A. i. i.) into its shell. From the muscular 

 gizzard the long narrow intestine (122. A. d. e. f.) makes 

 a double turn round the lobes of a small liver, and continues 

 nearly of uniform thickness to its termination on the right 

 side of the neck under the right branchial fin. The mouth 

 of the pneumodermon is furnished with two lateral retractile 

 tentacular tufts composed of minute pedunculated suckers 

 resembling those of a naked cephalopod, and two long and 

 wide salivary follicles which dilate each into a small sac 

 before they open into the muscular buccal cavity. The 

 surface of the tongue is covered with small sharp recurved 

 spines, and the capacious membranous stomach is perforated 

 with numerous minute openings of the enveloping lobes 

 of the liver as in many of the acephalous mollusca. 



XVIII. Cephalopoda. These animals being mostly free, 

 naked, and predaceous, are provided with powerful organs of 

 prehension and of mastication, and their short alimentary 

 canal is furnished with highly developed salivary, biliary, 

 and pancreatic glands. The mouth, surrounded by strong 

 muscular feet, and bordered by minute labial tentacular 





