VERTEBRATE ANIMALS MAMMALIA DIAGRAM 3. 27 



The sub-kingdom Mollusca only contains one class, that of the 

 molluscs. Their skin is always soft, with no appearance of 

 rings ; the greater part are protected by a stony substance, some- 

 times rolled into a spiral form, as in the snail, and sometimes 

 forming two separate parts called valves, as in the mussel. 



Lastly, the sub-kingdom Radiata comprises animals which are 

 constructed nearly like flowers, and all the parts of which radiate 

 from a common centre. The madrepores and corals belong to 

 this sub-kingdom. 



VERTEBRATE ANIMALS. 



CLASS MAMMALIA. 

 [ DIAGRAM 3. ] 



The first class among the Vertebrata is that of the Mammalia. 

 Their name means "having teats." They all bring forth and 

 suckle their young. They have generally four limbs, and are 

 covered with hair or spines. Nevertheless, there are mammals, 

 which we shall mention further on, which have no hair, and 

 resemble fishes externally. In many of them the vertebral 

 column extends beyond the pelvis, forming a tail. The number 

 of young which mammals can produce at a birth is very variable 

 the goat, the ass, the ewe, the mare, and the cow, have generally 

 only one ; the hare three or four ; the dog and cat five or six ; 

 the sow as many as fifteen. 



The Mammalia are divided into several orders. 



1st. The Quadrumana, or four-handed animals, which includes 

 all the apes. 



