i86o-6i 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 
