THE MONOTKEMA, OR CLOACAL ANIMALS. 87 



to be the connecting links between the Mammals, 

 Birds, and Eeptiles.' That he should regard 

 them as connecting links is certainly somewhat to 

 the point, only the Birds must be left out of the 

 question. A direct connection between Bird and 

 Mammal there is not ; they are allied through 

 their ancestors, and the latter stand widely sepa- 

 rated, although within the extremely comprehensive 

 order of Amphibio-reptiles. 



Their beak-shaped jaws do not possess any 

 teeth ; only in the case of the Duck- mole do we find 

 a few horny plates. This want of teeth has per- 

 haps been inherited from reptile-like ancestors, and 

 must have been distinct from the ancestors of the 

 toothed mammals; hence it would be a case of 

 convergence. The possible case of the common 

 origin of Duck-moles and of Toothed mammals from 

 primary forms of toothless animals, and of the 

 acquisition of teeth by Mammals independent of 

 toothed ancestors, is in the highest degree im- 

 probable ; or else the loss of the teeth may have 

 occurred only at a later period, after a common 

 origin on the line of duck-moles, as in the case of 

 Birds and various Edentates, partially also in the 

 upper jaw of the Hoofed Animals, and in all cases 

 of the reduction in the number of teeth. We take 



