CLASSIFICATION. 



27 



cold ; circulation double and incomplete ; heart with three 

 cavities ; respiration pulmonary, and simple. 



FOURTH CLASS. FISH. 



Oviparous; skin naked or furnished with scales; blood 

 cold ; circulation double and complete ; heart with two cavi- 

 ties ; respiration aquatic, by branchiee. 



Second Great Division. Anirnalia Mollusca — Molluscous or 



Soft Animals. 



Neither interior nor exterior skeleton ; body enveloped in 

 a soft and contractile skin to which the muscles are attached. 

 This skin, in many species, encrusts itself with stony matter 

 forming a kind of plate denominated shell. Nervous system 

 composed of many scattered masses, joined by nervous threads, 

 the chief of which is placed upon the oesophagus, and have 

 the name of brain. No special organ for smell, very seldom 

 for hearing, and often none for sight. Circulation complete; 

 blood white; generally a bluish white. Respiration effected 

 sometimes in a kind of pulmonary cavities ; more often by 

 branchiae. Seldom members for locomotion. 



Division of Mollusca into Three Classes. 



FIRST CLASS. CEPHALOPODA. 



Head very distinct, surmounted with fleshy arms, flexible 

 in every direction, and serving either for progress or for the 

 seizure of an object ; the rest of the body inclosed in a 

 rounded sack. Circulation double; respiration by branchire. 



SECOND CLASS. GASTEROPODA. 



A fleshy disk, upon which they crawl, is placed under the 

 abdomen. Head more or less distinct, provided with one or 

 more pairs of tentacula or feelers ; respiration pulmonary or 

 branchial. 



THIRD CLASS. ACEPHALA. 



No distinct head nor feelers ; mouth concealed with the 

 body in a mantle which is divided into two lobes. 



