82 THE GENESIS OF SPECIES. [Chap. 



placentals may have respectively descended from the car- 

 nivorous, insectivorous, and herbivorous marsu])ials. 



Among otlier 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 exam})les 

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

 marked that the insectivorous marsupials, e. g., Pcnundc^^ 

 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 [Jfacropodidtt) 

 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 susj)ect 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 ])arwinians, 

 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 



* " Journal of Anatomy and Physiology " (18G8), vol. ii., p. 139. 



