ANIMALIA VERTEBRATA. 5 



PISCES (fishes) may be described as oviparous animals, with cold and 

 red blood ; with a bilocular heart, that is, a heart consisting of one 

 auricle, and one ventricle ; breathing by permanent branchiae, or gills ; 

 with extremities modified into fins, for aquatic progression ; having the 

 body covered with scales ; bones more or less cartilaginous ; the vertebrae 

 with a funnel-shaped cavity on each articular surface, filled with an 

 elastic intervertebral substance, on which, as on a sort of cushion, each 

 vertebra moves ; the mouth destitute of salivary glands ; the teeth nu- 

 merous, and irregular ; no external ears ; the eyes destitute of eye- 

 lids. Respiration is effected by the transmission of water through 

 the mouth, over the surface of the fringe-like branchiae ; and the blood is 

 transmitted to the gills from the ventricle, whence, instead of returning 

 immediately to the heart, it is conveyed, by the branchial veins, to the 

 body : these veins, after giving branches to the anterior parts, unite to 

 form the aorta, which sends the arterialized blood through the rest of 

 the system, without the aid of a systemic heart : the brain does not fill 

 the cavity of the cranium ; it consists of a medulla oblongata, optic lobes 

 of great magnitude, cerebral hemispheres, olfactory tubercles, and a 

 cerebellum. 



AMPHIBIA. Oviparous vertebrate animals, with cold and red blood, 

 and with a naked skin ; commencing life as aquatic beings, immediately 

 after exclusion from the egg, and sometimes continuing aquatic through 

 life. They have, therefore, when young, branchiae, by which to breathe, 

 and a bilocular heart like that of a fish, together with a cup-shaped 

 cavity on each articular surface of the bodies of the vertebrae. The 

 greater number of Amphibia, as the Frog, Toad, and Newt, are caduci- 



matter does not assume the form of threads, as it does in the higher cycloneurose animals (Sea- 

 stars, for instance), but is diffused through their homogeneous composition. The following is an 

 arrangement given in a Course of Lectures by Professor Owen : 



ANIMALIA. 

 I. Subregnum ACRITA. 

 Classis 1. Polygastrica. Classis 4. Sterelmintha (Tape-worms, &c). ; 



2. Spongiae. 5. Acalephae. 



3. Polypi. 



II. Subregnum NEMATONEURA (NJj^ia, a thread, Net/pov, a nerve). 



Classis' 6. Echinoderma. Classis 8. Epizoa (external parasites). 



7. Coelelmintha (transparent soft 9. Rotifera. 



cavitary intestinal worms). 



III. Subregnum HOMOGANGLIATA, ('O/*os-, a pair, or two alike, Ta^Xiov, the knot of a nerve.) 

 Classis 10. Cirripeda. Classis 13. Arachnida. 



11. Annelida. 14. Crustacea. 



12. Insecta. 



IV. Subregnum HETEROGANGLIATA ('Erepoy, other, 'ErepoTnr, diversity). Taj^Xiov. 

 Classis 15. Tunicata. Classis 18. Pteropoda. 



16. Palliobranchiata. 19. Gasteropoda. 



17. Lamellibranchiata. 20. Cephalopoda. 



V. Subregnum VERTEBRATA. 

 Classis 21. Pisces. Classis 23. Aves. 



22. Reptilia. 24. Mammalia. 



