82 THE GENESIS OF SPECIES. [CHAP. 



placentals may have respectively descended from the car- 

 nivorous, insectivorous, and herbivorous marsupials. 



Among other points Prof. Huxley called attention to 

 the resemblance between the anterior molars of the placen- 

 tal dog with those of the marsupial thylacine. These, in- 

 deed, are strikingly similar, but there are better examples 

 still of this sort of coincidence. Thus it has often been re- 

 marked that the insectivorous marsupials, e. g., Perameles, 

 wonderfully correspond, as to the form of certain of the 

 grinding teeth, with certain insectivorous placentals, e. g., 

 Urotrichus. 



Again, the saltatory insectivores of Africa (Macrosce- 

 lides) not only resemble the kangaroo family (Macropodidce) 

 in their jumping habits and long hind-legs, but also in the 

 structure of their molar teeth, and even further, as I have 

 elsewhere * pointed out, in a certain similarity of the upper 

 cutting teeth, or incisors. 



Now, these correspondences are the more striking when 

 we bear in mind that a similar dentition is often put to 

 very different uses. The food of different kinds of apes is 

 very different, yet how uniform is their dental structure ! 

 Again, who, looking at the teeth of different kinds of bears, 

 would ever suspect that one kind was frugivorous, and 

 another a devourer exclusively of animal food ? 



The suggestion made by Prof. Huxley was therefore 

 one which had much to recommend it to Darwinians, 

 though it has not met with any notable acceptance, and 

 though he seems himself to have returned to the older no- 

 tion, namely, that the pouched-beasts, or marsupials, are a 

 special ancient offshoot from the great mammalian class. 



But, whichever view may be the correct one, we have in 

 either case a number of forms similarly modified in har- 

 mony with surrounding conditions, and eloquently proclaim- 

 ing some natural plastic power, other than mere fortuitous 



4 " Journal of Anatomy and Physiology " (1868), vol. ii., p. 139. 



