26 MAMMALIAN DESCENT. [LECT. II, 



the bottom of the Secondary rocks may belong to 

 some simple primordial mammal, and not to a proper 

 Marsupial. If this be so, we may have in those most 

 precious, but also most puzzling, remains, the evidence of 

 the existence of Prototheria (first beasts) with true teeth. 



The living forms of these Prototheria are either tooth- 

 less, as the Echidna, or have only peculiar horny plates,, 

 as a succedaneum to true teeth, as in the Ornithorhynchus. 



That, at present, we are in the dark as to the early 

 existence of forms of such surpassing interest to the 

 Darwinian, is no proof that they have not had their day, 

 and their reign, or dynasty, in this part of the world, 

 long before the higher, or even the Marsupial, mammala 

 appeared. For negative evidence is literally no evi- 

 dence at all in matters of this kind. A few years ago- 

 we had no evidence of the existence, in the geological 

 strata, of birds with true teeth, nor of birds with a long 

 chain of caudal vertebrae, and distinct metacarpals. 

 Now, however, two new additional orders of the bird 

 class are known to have existed in the Secondary epoch, 

 one as far below the other as the higher of the two is- 

 below ordinary flying birds ; the newest of these kinds 

 possessed teeth, and the lowest the Archceopteryx had 

 the metacarpals, jor bones of the hand, distinct, and the 

 joints of its tail developed and elongated, whereas in 

 existing birds they are aborted. 



All attempts at keeping back the tide of modern 

 biology are but imitations of the labours of Sisyphus ; 



