FI^H OR FLESH 321 



water and snakes on land, wliile with birds some live 

 wholly on land and a few mostly on the water. 



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

 blooded order of Mammals, we usnally think only 

 of animals with four legs, quadrupeds as they are 

 called. But an Alligator is a quadruped without being 

 a Mammal, and 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. AVhat 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 tliere 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, 

 thougli I Its face looks like one of tliose big tomato 

 worms." 



"We thought the Walrus hideous and grotesque, and 

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



