﻿MONOTREMES. 225 



their radical distinction from both the latter groups. Accord- 

 ingly it has been proposed to brigade both the Pouched and 

 the Placental Mammals in one grand division of the class, and 

 to make the Egg-laying Mammals the sole representatives of a 

 second division of similar rank. Although there is a good deal 

 to be said in favour of such a binary division of the Mammalian 

 class, yet as the ternary division has been almost universally 

 adopted, it seems a pity to disturb it, more especially as it 

 serves all the purposes of classification. In following such a 

 ternary arrangement, all that the student has to bear in mind is 

 that the gap separating the third sub-class from the second is 

 vastly greater than that by which the first and second are 

 . sundered. 



With these general preliminary remarks, we may proceed to 

 the consideration of the characters by which the aforesaid 

 Monotremes or Egg-laying Mammals are thus sharply dis- 

 tinguished from all other living representatives of the class. It 

 may be mentioned, however, that it is only comparatively 

 recently that it has been definitely ascertained that these 

 strange Mammals, although nourishing their young with milk 

 secreted from special glands on the body of the female parent, 

 after the manner of the rest of their class, yet actually lay eggs 

 like a Bird or a Reptile. Reports were, indeed, brought home by 

 those who had interviewed the aborigines of Australia as to the 

 oviparous habits of one at least of these animals, but these 

 were generally discredited either by the interviewers themselves, 

 or by those to whom the story was reported. Still, however, 

 even among anatomists and zoologists themselves there seems 

 to have been a lingering suspicion that there was something 

 peculiar about the reproduction of these antipodean creatures. 

 For instance, Meckel the anatomist, who first proved the 

 existence in one of them (the Duck-bill) of mammary or milk- 

 glands, still doubted whether the animal might not lay eggs 

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