10 VBBTEBBATB ATsmwAT.g. 



eight classes. These are: — 1. Mammalia, or Mammals; 

 2. AvES, or Birds; 3. Reptilia, or Reptiles; 4. Batkachia, 

 or Batrachians; 5. Pisces, or True Fishes; 6. Elasmo- 

 BRANCHii, or Selachians ; 7. MAESiPOBEAif chii, or Myzonts ; 

 8. Leptocaedii, or Lancelots. 



Of these classes, two, JElasmohranchii and Leptocardii, 

 are represented by marine forms only, and do not, 

 therefore, come within the scope of this treatise. 



The relations of the classes of Vertebrates may be 

 recognized by the following analysis, taken, in part, 

 from Prof. Grill's "Arrangement of the Families of 

 Fishes." Only the most obvious characters are here 

 referred to, although others, less striking, are often of 

 greater taxonomic value. 



CLASSES OF VERTEBRATES. 



* Respiration never performed after birth by means of branchiae. 

 f Exoskeleton developed as hair (rarely obsolete) ; warm blood ; 

 heart with four cavities ; diaphragm complete ; two occipital 

 condyles ; viviparous ; young developed from' a minute egg, 

 and nourished for a time by milk secreted in the mammary 

 glands of the mother. .... Mammalia. 

 ff Exoskeleton developed as feathers; warm blood; heart with 

 four cavities; diaphragm incomplete; a single occipital 

 condyle ; oviparous ; young hatched from a comparatively 



large egg; no mammary glands Aves. 



ttf Exoskeleton developed as scales, or bony plates ; cold blood ; 



heart with three cavities (four in Orocodilia); a single 



occipital condyle ; oviparous (or rarely ovoviparous) ; young 



hatched from a rather large egg. . . . Reptilia. 



** Respiration performed by gills for a part, or the whole, of life ; 



cold blood. 



% Skull more or less developed, with the notochord not continued 



forwards beyond the pituitary body; brain diflferentiated 



and distinctly developed; heart developed and divided 



into at least an auricle and ventricle. 



