PHYLUM CHORDATA 



401 



Class V. REPTILIA (Lat. repere, to crawl) . SPHENODON, 

 CHAMELEONS, LIZARDS, SNAKES, CROCODILES, and TURTLES 

 (Figs. 439-469). Cold-blooded vertebrates breathing by means 

 of lungs and usually having a scaly skin. 



Class VI. AVES (Lat. avis, bird). BIRDS (Figs. 470-509). - 

 Warm-blooded vertebrates with the fore limbs modified into 

 wings and the body covered with feathers. 



Class VII. MAMMALIA (Lat. mamma, breast). HAIRY QUAD- 

 RUPEDS, WHALES, SEALS, BATS, MONKEYS, and MAN (Figs. 510- 

 550). Warm-blooded vertebrates with a hairy covering at 

 some stage in their existence; the young nourished after birth 

 by the secretion of the mammary glands of the mother. 



Plan of Structure. The vertebrates resemble the other 

 chordates in their metamerism and bilateral symmetry and in the 



NEURALTUBE ( cffffBffo SPIN A L CANAL) . 

 SPINAL CORD yC NOTOCHORD VISCERAL 



BRAIN 



ORAL CAVITY 



INTERNAL GILL SLITS, 



HEART 



SPLEEN 



CLOACA 



URINARY BLADDER 



LIVEK 



'fliLE DUCT 

 PANCREAS 



FIG. 345. Diagrammatic longitudinal section of a vertebrate (female). 

 (From Wiedersheim.) 



possession of a ccelom, a notochord, and gill-slits at some stage 

 in their existence, and a dorsal nerve tube. They differ from other 

 chordates and resemble one another in the possession of carti- 

 laginous or bony vertebra, usually two pairs of jointed appendages 

 containing a central skeleton, a ventrally situated heart with at 

 least two chambers, and red corpuscles in the blood. 



2 D 



