MAMMALIA, 465 
The temperature of reptiles is directly dependent upon 
that of their surroundings, but that of mammals and birds 
is constant—that is to say, the heat-producing agencies of 
the body are so adjusted that the body-temperature is 
maintained at a certain mean average. That of birds is 
much higher than that of mammals, and for this reason the 
body-temperature of birds is sometimes described as hot 
and that of mammals as warm. ‘The special point, however, 
is in each case the constancy of the temperature, whatever 
the environment. In this respect, as in many others, the 
Prototheria and Metatheria approach the reptilian condition. 
ALIMENTARY SysTEM.—The same general plan of ali- 
mentary system holds throughout, though certain changes 
are found in correlation to special methods of feeding. A 
number, such as the anteaters, pangolins and Zchidna, have 
an elongated protrusible tongue and highly developed 
salivary glands, the saliva being used to make the tongue 
sticky, by which means the ants and other insects may be 
readily caught. 
The stomach is more or less simple in some forms but 
extremely complex in others. The complexity is of two 
kinds. The first is its division into two or more chambers 
which are easily visible externally and the second involves 
the distribution of the glands. A more or less prominent 
part of the stomach which immediately succeeds the 
cesophagus has an entire absence of glands and is lined 
only by stratified epithelium. The whole stomach is of 
this nature in Ornithorhynchus. Again, this area is followed 
typically by an area containing cardiac glands, another 
containing fundus glands. and, lastly, by the hinder 
portion containing pyloric glands. The fundus glands may 
often be absent. 
The first division of the stomach is effected by a con- 
striction dividing it into cardiac and pyloric chambers, as in 
certain rodents. In most cases the cardiac portion has no 
glands, whilst cardiac and pyloric glands are found in the 
pyloric portion. In others, as the porpoise (p. 546), there 
are three chambers, consisting of a non-glandular cardiac 
part, a second chamber with cardiac glands and a small third 
and fourth with pyloric glands. In the Ruminants there’ 
M. 31 
