CHAPTER XIV 

 FISHES, BATRACHIANS, AND REPTILES 



The great branch of vertebrate or backboned animals 

 includes the classes of fishes, the batrachians, the rep- 

 tiles, the birds, and the mammals. All these possess a 

 bony (or cartilaginous) spinal column, which distinguishes 

 them from the invertebrates or backboneless animals. 

 In addition they possess a further internal bony skeleton 

 (cartilaginous in some fishes, as the sharks and sturgeons), 

 including in all but the most primitive forms two pairs of 

 appendages or limbs. In some these limbs are mere 

 rudiments, as in the snakes, where only a few (pythons) 

 show any external sign of them ; but in most vertebrates 

 they are well developed organs of locomotion, appearing 

 as fins in the fishes, as legs in the batrachians, reptiles, 

 and most mammals, as wings and legs in the birds, and 

 as arms and legs in the monkeys and man. In almost 

 all vertebrates the blood is red, and is always confined in 

 a special circulatory system consisting of heart, arteries, 

 veins, and capillaries. Air is taken up by the gills or 

 lungs, to which the blood is brought to be purified, i.e., 

 to give up its carbon dioxide and receive oxj^gen. The 

 nervous system is highl}' developed, with a large brain 

 and with complex and highly efficient sense-organs, as 

 eyes, ears, etc. 



Except for the insects the vertebrates include most of 

 the animals we familiarly know. They are pre-eminently 

 the "intelligent animals" (ants, bees, and wasps, and 

 some other insects and spiders are also, of course, in- 



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