BIRDS. 



(a) Eutheria, Monodelphia, or Placentals— those in which there is a 



close (placental) union between the unborn embryo and its 

 mother, e.g. Ungulates, Carnivores, Monkeys. 



(b) Metatheria, Didelphia, or Marsupials— the prematurely bearing, 



usually pouch-possessing kangaroos, opossums, etc. 



Fig. 2. — Phenacodus, a primitive extinct Mammal. — After Cope. 



(<r) Prolotheria, Ornithodelphia, or Monotremes — the egg-laying 

 duckmole ( Ornithorhynchus), Echidna, and Proechidna. 



Birds. — There can be 

 no hesitation as to the 

 class which ranks next to 

 Mammals. For Birds are 

 in most respects as highly 

 developed as Mammals, 

 though in a different direc- 

 tion. They are character- 

 ised by their feathers and 

 wings, and many other 

 adaptations for flight, by 

 their high temperature, 

 by the frequent spongi- 

 ness and hollowness of 

 their bones, by the tend- 

 ency to fusion in many 

 parts of the skeleton, 

 by the absence of teeth 

 in modern forms, by 

 the fixedness of the 

 lungs and their associa- 



FlG. 3. — Extinct moa and modern 

 kiwi. — After Carus Sterne. 



tion with numerous air sacs, and so on. 



