l6o THE STORY OF ANIMAL LIFE 



iridescent feathers. Like the iridescence of the 

 Rainbow Worm, they fall short of absolutely 

 metallic brightness ; the fault in this case being 

 due not to the nature of the underlying stratum, 

 so much as to the incomplete development of the 

 light-reflecting grooves. Yet this instance serves 

 to show the part taken by the dark pigment ; 

 for while the play of colours is perfectly obvious 

 in the fur of a black cat, it is almost impossible 

 to distinguish it in the case of cats with fur of 

 lighter shades. 



The Mammalia, or animals that suckle their 

 young and produce them by birth, were formerly 

 considered to be sharply defined from animals 

 that lay eggs, such as the birds and reptiles. 

 But in 1884 Mr. Caldwell confirmed the state- 

 ment which had been made previously, yet hardly 

 credited by the scientific world, to the effect that 

 the lowest form of mammals lays eggs. This, 

 the Duck-Mole or Ornithorhyncus anatinus (Bird- 

 billed animal much like a goose), is a native of 

 Australia and Tasmania. It lives on the banks 

 of rivers, and burrows in the bank. It has 

 webbed feet, and therefore sometimes receives 

 the name of Platypus (flat-foot). It lays eggs 

 two at a time, in its burrow ; and these eggs, 

 like those of other egg-laying vertebrates, have a 

 yolk. 



A kindred form, Echidna hystrix or Spiny 

 Ant-eater, is found in Australia, Tasmania, and 

 New Guinea. The Echidna hatches its young in 

 a temporary pocket, which appears in the neigh- 

 bourhood of the breasts, and disappears after the 

 young are old enough to take care of themselves. 

 The Ornithorhyncus has fur, the Echidna has spines, 

 with hairs between them. Neither bears the slight- 



