112 



ANIMAL KINGDOM. 



compound eyes, more than four pairs of legs, 

 the respiration effected by gills, and the shell 

 generally hard and calcareous. These ento- 

 moid aquatic animals are generally carnivorous, 

 and have a short and straight alimentary canal. 

 Their circulating system is often aided by a 

 muscular ventricle. The sexes are separate, 

 and the organs of generation are double and 

 symmetrical in both sexes. Their biliary or- 

 gans have a conglomerate form, being com- 

 posed of minute glandular follicles grouped 

 together into lobules and larger lobes. Some 

 of these animals are fixed and parasitic, and 

 breathe by their general exterior surface ; most 

 are free, and respire by means of branchiae 

 placed under the sides of the carapace or ex- 

 posed on the under-surface of the post-abdomen. 

 (See CRUSTACEA.) 



The THIRD, or CYCLO-GANGLIATED or mol- 

 luscous DIVISION of the animal kingdom, com- 

 prehends five classes, viz. : 



14. Tunicata, soft, aquatic, acephalous 

 animals, breathing by internal branchiae, never 

 in form of four pectinated laminae, and covered 

 by a close external elastic tunic furnished with 

 at least two apertures. The exterior tunic is 

 lined by a muscular coat ; sympathetic ganglia 

 are observed in the abdominal cavity, and the 

 respiratory organs are ciliated as in higher 

 molluscous classes for the production of the 

 respiratory currents. The mouth, unprovided 

 with tentacula or other organs of sense, opens at 

 the bottom of the abdominal cavity, as seen in the 

 cynthia dione. (Fig. 39. a.) The short cesopha- 



Fig. 39. 



Fig. 40. 



gus leads to a capacious stomach (b), sometimes 

 surrounded by the lobes of a small liver, which 

 pours its secretion into that cavity as in higher 

 mollusca. From the stomach a short wide 

 convoluted intestine proceeds to near the ven- 



tral orifice (d*) of the sac, where it terminates 

 in the anus (c). The thoracic orifice (e), or the 

 entrance to the respiratory cavity, is generally 

 provided with numerous delicate tentacula ( /'), 

 and a nervous longitudinal filament (A) is ge- 

 nerally observed to encompass that opening, and 

 to terminate in a small glanglion (g). These ani- 

 mals are entirely marine, most are fixed, some 

 are free ; they are all female, like the conchifera ; 

 the circulation is aided by a muscular heart. 

 Many are organically connected in groups, 

 others are isolated, (See TUNICATA.) 



15. Conchifera, acephalous, aquatic ani- 

 mals, covered with a solid calcareous shell, 

 consisting of at least two pieces, and breathing 

 by internal branchiae in form of four pectinated 

 laminae. These bivalved animals have the 

 mouth, as in the former class, situated at the 

 bottom of the respiratory or thoracic cavity; 

 the stomach is surrounded and perforated by 

 the lobes of the liver ; the circulation is aided 

 by a bifid or a divided auricle and by a mus- 

 cular ventricle, which is generally perforated 

 by the rectum, as seen in the annexed figure of 

 the organs of the spondt/lus, (Jig. 40.) The 



two fimbriated lips 

 (a) which surround 

 the mouth are pro- 

 longed laterally into 

 four tapering flat pec- 

 tinated tentacular ex- 

 pansions (b) . The 

 stomach (c) and the 

 intestine are sur- 

 rounded by the large 

 mass of the liver (i), 

 and the rectum, near 

 the adductor muscle 

 (m), penetrates the 

 ventricle of the heart 

 (d), at some distance 

 from the anus (ej. 

 The branchial veins 

 (g, h) return the 

 aerated blood to the 

 two lateral divisions 

 of the auricle, these 

 pour it into the ventri- 

 cle, by which it is pro- 

 pelled forwards and 

 backwards through 

 the system, so that the heart is here, as in 

 other invertebrated classes, a systemic organ. 

 (See CONCHIFERA.) 



16. Gasteropoda, body invertebrate and in- 

 articulate, provided with a head which for the 

 most part supports tentacula and simple eyes, 

 and furnished with a muscular foot, extended 

 under the abdomen, and adapted for creeping. 

 These animals are sometimes naked, more 

 generally covered with a univalve, unilocular, 

 solid, external shell. Some gasteropods breathe 

 by a pulmonary cavity, most by branchiae va- 

 riously disposed on the surface or under an 

 open mantle. Most are marine, many inhabit 

 fresh waters, and some reside on land. The 

 higher forms are mostly carnivorous, and the 

 lower orders phytophagous, and this difference 

 affects principally their alimentary apparatus, 



