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 

 Frototheria 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 Echidna, 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 

 oesophagus 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 /^y/c?/-/^ 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 



