FISH OB FLESH 321 



water and snakes on land, while with birds some live 

 wholly on land and a few mostly on the water. 



" Of course when we speak of the milk-giving, warm- 

 blooded order of Mammals, we usually think only 

 of animals with four legs, quadrupeds as they are 

 called. But an Alligator is a quadruped without being 

 a Mammal, aud a Whale is a Mammal without being a 

 quadruped." 



"It's a kind of a puzzle how it can be, isn't it? " said 

 Nat. 



"Not if you remember m — mammals, m — milk," said 

 Dodo, quickly. 



"You must have often heard the saying that 'the 

 exception proves the rule,' " continued the Doctor ; " so 

 the story of these footless ones is the exception to prove 

 that four feet are the rule among Mammals. Look at 

 your Mammal tree. What is the lowest branch of all? " 



"Pouch wearers," said Nat, "are on the lowest 

 branch that grows with us, though there are two others 

 lower that are only stumps. Opossum is the pouch 

 wearer, but there is a picture of him in the portfolio, 

 and'he has four legs and a curly tail. Why is he lower 

 than no-legged beasts ? " 



"I will tell you that when we- come to him. What 

 is the next branch ? " 



"Sea Cows; and the ladder says there is only one 

 species in North America and its name is Manatee, 

 and that it is eight or ten feet long. Isn't it ugly, 

 though! Its face looks like one of those big tomato 

 worms." 



" W^ thought the Walrus hideous and grotesque, and 

 the Sea Lion awkward," said the Doctor ; " but what 



