6 THE INFANCY OF ANIMALS 



knowledge that the bird is hatched from an 'egg, after a 

 more or less prolonged period of brooding on the part of 

 one or both of the parents : while in the reptiles and the 

 more lowly vertebrates no brooding is necessary — though, 

 as we shall show, the eggs are often jealously guarded and 

 tended. 



Now the birds and the mammals are both descendants 

 of the more lowly reptiles ; but have developed along 

 very different lines. But, great as their transformation 

 has been, each retains more or fewer records in their 

 structure affording indubitable proof of the source of 

 their being. Among the higher mammals, however, these 

 proofs of parentage have in the course of ages grown 

 more and more illegible, and but for the clues presented 

 in the more lowly types these evidences of past happenings 

 might well escape discovery altogether. Happily for' us, 

 however, in certain lowly creatures, to wit the Australian 

 duck-billed platypus, or ornithorhynchus, and the spiny 

 ant-eater, or echidna, evidences of this reptiUan ancestry 

 are writ large in their bony framework ; and hence, long 

 since, it became apparent that the lord of creation himself 

 is not merely a blood-relation of the ape, but is the last 

 term of a series of evolutionary changes which began with 

 the beginnings of the despised and cold-blooded reptiles ! 



The full force, however, of this conviction was not 

 realised until a few years ago, when, in 1884, the amazing 

 discovery was made that these same lowly mammals 

 presented a still more significantly reptihan feature in 

 that their young were hatched from eggs ! The hall- 

 mark of the mammal, however, was readily apparent, for 

 it was at once established that the young were nourished 

 by milk secreted by the mother. Very well. We have 

 just remarked that the condition^of the young at birth 



