ANIMAL KINGDOM. 



113 



as seen by comparing that of the carnivorous 

 buccinurn undatum, (flg.4l,) with the same 



Fig. 41. 



apparatus in the phytophagous patella vulgata, 

 fjig. 42.) Like most of the predaceous gas- 

 teropods the buccinum is provided with a long 

 muscular proboscis, (fig. 41, a, b,) capable of 

 being extended to a distance from the mouth, 

 and enclosing a bifid tongue covered with sharp 

 recurved teeth. The oesophagus near the sto- 

 mach dilates into a small crop (c), and to this 

 succeeds a round membranous stomach (d, e). 

 The whole remaining intestine is shorter than the 

 oesophagus, and dilates into a wide colon (J',~) 

 before terminating in the anus (g), on the right 

 side of the body under the open mantle. The 

 liver, of great size, and accompanying the 

 testicle (i) in the turns of the spire, pours 

 its secretion into the stomach as in the acepha- 

 lous classes. The vas deferens following the 

 right side of the body terminates at the end of 

 the male organ (A) in a small tubular styhform 

 duct. In the patella, (Jig. 42,) however, which 

 feeds on marine plants, the mouth (a) is provided 

 with a long slender convoluted tongue covered 

 with numerous rows of teeth like a long file. 

 The wide and sacculated oesophagus (d) leads 

 to a capacious and lengthened stomach (f, g), 

 surrounded by the large liver, and the' long 

 convoluted intestinal canal (h) makes several 

 turns imbedded in the mass of the liver before 



it arrives at the short 

 Fig. 42. dilated rectum (i) 



and anus (/c). The 

 salivary glands are 

 generally of great 

 size in this class, 

 and present some- 

 times in the same 

 species both the 

 simple follicular 

 and the conglome- 

 rate forms. The 

 pancreas likewise is 

 often present in form 

 of a single follicle 

 opening into the sto- 

 mach along with the 

 biliary ducts. The 

 inferior orders are mostly male and female, but 



VOL. I. 



in the higher forms the sexes are distinct. (See 

 GASTEROPODA.) 



17. Pteropoda, body organized for swim- 

 ming, mantle closed above, branchiae external, 

 no muscular foot for creeping, shell, when 

 present, always thin, pellucid, unilocular, and 

 inoperculate. These soft, minute, floating ani- 

 mals are all marine, and are enabled to swim 

 by means of two lateral musculo-cutaneous fin- 

 like expansions, on the surface of which the 

 respiratory branchiae or vascular plexuses are 

 placed. These lateral fins are never supported 

 by rays. The head is generally provided with 

 retractile or sheathed tentacula, seldom with 

 eyes. The body is sometimes entirely naked, 

 often protected by a delicate thin transparent 

 shell,which encloses tlie abdomen and is covered 

 with a fold of the skin. They appear to be most 

 closely allied to the inferior testaceous cepha- 

 lopods in the nature and form of their shells 

 and in their locomotive powers, and also in 

 the general simplicity of their internal struc- 

 ture, especially of their generative organs. The 

 structure of one of the naked pteropods, clio 

 boreulis, is represented in fig. 43, where the 

 abdominal cavity is exposed by the mantle 



Fig. 43. 



Vfc 



being opened from behind. The mouth (a) 

 leads to a long esophagus (b), which is sur- 

 rounded by a circular series of nervous gan- 

 glia (t). The stomach (c c) is imbedded in the 

 lobes of the liver (g), which open by numerous 

 short ducts into its cavity. The oesophagus is 

 accompanied by the two long simple salivary 

 follicles (/c), and at the left or pyloric extremity 

 (d) of the stomach is placed the heart (j), en- 

 closed in its pericardium, which receives the 

 arterialized blood from the branchial veins, and 

 sends it through the system. The bottom of 

 the abdomen or cavity of the mantle (A) is 

 occupied as in the cephalopods with the gene- 

 rative organs, which consist of an ovary (/) 

 and long oviduct (m, o), into which a short 

 wide coscum (?), commonly considered as a 

 testicle, pours its secretion. The oviduct termi- 

 nates on the left side, near the anus (e), in a 

 small glandular sac (a), beneath which is the 

 rhenal sac (p). The pteropods are commonly 

 found floating in immense numbers at the sur- 



