CLASSIFICATION AND EVOLUTION 519 



limbs, horny scales, no median fins, 

 lungs, large, heavily yolked eggs laid 

 in calcareous shells, no larva, an amnion 

 and an allantois in the embryo, and 

 the gill-clefts never functional. 



The characteristic features of the following Orders of 

 Reptilia and examples of their members are given in 

 Chapter XXI. 



Lacertilia, Ophidia, Chelonia, Crocodilia, 

 Rhynchocephalia. 



e. Class Aves. 



Warm-blooded Vertebrata with penta- 

 dactyle limbs, of which the first pair 

 are wings, feathers and on the legs 

 horny scales, no median fins, lungs, 

 large, heavily yolked eggs laid in cal- 

 careous shells, no larva, an amnion 

 and an allantois in the embryo, and the 

 gill-clefts never functional, 

 e.g. Columba. 

 f. Class Mammalia. 



Warm - blooded Vertebrata with penta- 

 dactyle limbs, hairs, but no scales, 

 median fins only in some whales, where 

 they have no rays, lungs, eggs almost 

 always minute, developing within the 

 mother, milk - glands, no larva, an 

 amnion and an allantois in the embryo, 

 and the gill-clefts never functional. 



The characteristic features of the following groups of 

 mammals are stated and examples of their members 

 mentioned in Chapter XXIV. 



i. Sub-class Prototheria. 



Order Monotremata. 

 ii. Sub-class Metatheria. 



Order Marsupialia. 

 iii. Sub-class Eutheria. 



Order Cetacea. 



Order Edentata. 



Order Sirenia. 



