112 



ANIMAL KINGDOM. 



compound eyes, more than four pairs of legs, tral orifice (rf) of the sac, where it terminates 



the respiration effected by gills, and the shell in the anus (c). The thoracic orifice (e), or the 



generally hard and calcareous. These ento- entrance to the respiratory cavity, is generally 



moid aquatic animals are generally carnivorous, provided with numerous delicate tentacula ( /'), 



and have a short and straight alimentary canal, and a nervous longitudinal filament (A) is ge- 



Their circulating system is often aided by a nerally observed to encompass that opening, and 



muscular ventricle. The sexes are separate, to terminate in a small glanglion (g). These ani- 



and the organs of generation are double and mals are entirely marine, most are fixed, some 



symmetrical in both sexes. Their biliary or- are free; they are all female, like the conchifera; 



gans have a conglomerate form, being com- the circulation is aided by a muscular heart, 



posed of minute glandular follicles grouped Many are organically connected in groups, 



together into lobules and larger lobes. Some others are isolated, (See TUNICATA.) 



of these animals are fixed and parasitic, and 15. Conchifera, acephalous, aquatic ani- 



breathe by their general exterior surface ; most mals, covered with a solid calcareous shell, 



are free, and respire by means of branchiae consisting of at least two pieces, and breathing 



placed under the sides of the carapace or ex- by internal branchiae in form of four pectinated 



posed on the under-surface of the post-abdomen, laminae. These bivalved animals have the 



(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 cular ventricle, which is generally perforated 



animals, breathing by internal branchiae, never by the rectum, as seen in the annexed figure of 



in form of four pectinated laminae, and covered the organs of the spondylus, (Jig. 40. ) 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- 



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. 



in 



I 



two fimbriated lips 

 (a) which surround 

 the mouth are pro- 

 longed laterally into 

 four tapering flat pec- 

 tinated tentacular ex- 

 pansions (b). The 

 stomach fcj 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 



gus leads to a capacious stomach (6), sometimes open mantle. Most are marine, many inhabit 

 surrounded by the lobes of a small liver, which fresh waters, and some reside on land. The 

 pours its secretion into that cavity as in higher higher forms are mostly carnivorous, and the 

 mollusca. From the stomach a short wide lower orders phytophagous, and this difference 

 convoluted intestine proceeds to near the veo- affects principally their alimentary apparatus, 



