CHAPTER XXVI 



CLASS MAMMALIA. 1 



As Birds and Mammals have evolved along very different 

 lines, Birds possessing the air and Mammals the earth, it is 

 difficult to say that either class is the higher. But apart 

 from the fact, which prejudices us, that man himself is 

 zoologically included among Mammals, this class is superior 

 to Birds in two ways in brain development and in the 

 relation between mother and offspring. In most Mammals 

 there is a prolonged organic connection between the mother 

 and the unborn young, and perhaps Robert Chambers was 

 right in suggesting that this prolonged gestation was one of 

 the conditions of progress, connected, it may be, with the 

 development of large brains. Moreover, it is characteristic 

 of Mammals that the young are nourished after birth by 

 their mother's milk, and it has been suggested that the 

 prolonged infancy of young Mammals was one of the factors 

 in the evolution of gentleness. It is certain at least that 

 the carefulness and sacrifice of the mothers has been a 

 condition of the survival and success of Mammals, and of 

 Birds also. We may find in the term Mammalia, which 

 Linnaeus first applied to the class, a hint of the idea that in 

 the evolution of these forms of life, the mothers led the 

 way. 



General Survey of Mammals. 



There are three grades of Mammalian development : 

 (A.) The duckmole (Ornithorhynchus) and the spiny ant- 



1 In the systematic part of this chapter I have been especially in- 

 debted to the " Introduction to the Study of Mammals" by Sir W. H. 

 Flower and Mr. Lydekker. (Lond., 1891.) 



