MONOTREMES, 225 
to make the Egg-laying Mammals the sole representatives of a 
second division of similar rank. Althou 
} their radical distinction from 
| to be said in favour of such a binary division of the M 
| 
| 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 
For instance, Meckel the anatomist, who first proved the 
>xistence in one of them (the Duck-bill) of mammary or milk- 
lands, still doubted whether the animal might not lay eggs 
2 Q 
