1860-61 LECTURE AT NORWICH 119 



temperature, which was usually higher than the 

 temperature around them. These were the 

 cold-blooded and warm-blooded vertebrates. One 

 class produced eggs, the other produced living 

 young. Some moved on four limbs, others on 

 two ; some had no lower limbs, properly so called. 

 Aristotle had divided the group into bipeds, quad- 

 rupeds, and impeds. The quadrupeds formed 

 the great bulk. The impeds living in the sea, 

 as fishes, were warm blooded and breathed air ; 

 the bipeds were ourselves. 



The quadrupeds were so large a proportion that 

 it was necessary to subdivide them ; and Aristotle 

 had said of them that one-half had their limbs 

 terminating with digits ending in claws or nails, 

 while the others had the ends of the digits 

 enclosed in a horny thimble or hoof. Conse- 

 quently, he divided them into the hoofed and 

 clawed quadrupeds. The hoofed quadrupeds he 

 divided according to the number of the divisions 

 of the hoofs, and the others he divided according 

 to their dentition, as carnivorous, graminivorous, 

 and so on. Linnaeus was the first who definitely 

 and properly divided the mammalian groups, and 

 it was he who gave them the name Mammalia. 

 The Mammalia also were characterised not only 

 by having living young, but by nourishing their 

 young in a peculiar way. Another characteristic 

 was that of having hair upon their bodies, for 

 those that were not covered with hair were 



