PLATYPUS AND ECHIDNA 



lively mammalian but appertain to the lower lying 

 amphibians and reptiles, are important indications of 

 the grade of the mammal concerned. Now perhaps no 

 two mammals are more diverse in outward appearance 

 and even in many anatomical details than the spiny 

 ant-eater of Australia, and the duck-billed platypus 

 of the same continent. 



The one is spiny, toothless, long-snouted, long- 

 tongued ; the other furry, " duck-billed," web-footed ; 

 their skeletons and internal organs differ widely, and 

 yet in both of these creatures the young are hatched 

 from large eggs with much yolk, and there is no con- 

 nexion between the young and the mother, the eggs 

 leaving the body as eggs. Furthermore, there is a 

 peculiar vein, or traces of it, which is quite like a vein 

 found in the lower vertebra ta, but not represented in 

 the higher mammals, and the structure of the heart shows 

 an analogous state of affairs. All these points link the 

 Monotremata, as the order comprising these the only 

 two existent types of the order is called, together ; they 

 have been arrested, as it were, before they have com- 

 pletely thrown off the characters of the amphibio- 

 reptile from which the mammalia have in course of time 

 been evolved. We must therefore clearly set apart those 

 two forms into a group by themselves. The remaining 

 mammals, the vast majority of course, can hardly be 

 sorted into an ascending series, getting less and less 

 reptilian. Palaeontology, moreover, while explicit as to 

 the relationships of certain groups, is at present cloudy 

 as to the derivation of the higher mammals, or Eutheria 

 as they have been termed, from the Monotremata, the 

 only surviving members of the early mammals, or 

 Prototheria. All the Eutheria contrast with the 

 Prototheria in having minute eggs which are not " laid," 

 but develop inside the body of the parent, and come 

 to be attached to the tissues of the mother, deriving 

 Z.G. 17 C 



