96 THE MAMMALIA. 



can be no reasonable doubt that the existing Mar- 

 supials have undergone a like suppression of the 

 deciduous teeth in the course of their development 

 from ancestors which possessed a full set.' If this 

 is the right explanation, the suppression of the 

 milk teeth in Marsupials must be transferred to 

 a comparatively more recent period when the 

 branching off of the Eutheria, which still possess 

 the milk teeth, had not yet taken place. A proof 

 of this is that some groups of Mammals do not 

 show this succession of milk teeth and permanent 

 teeth, or rather that they have lost it notwith- 

 standing a relationship marked by a change of 

 teeth. 



As regards teeth and limbs, the Marsupials 

 of to-day bear testimony to no small amount of 

 adaptability. It may be compared with that 

 adaptability which is evident in the whole class of 

 the higher Mammals, if we are not to admit that 

 the Eutheria have originated separately in groups 

 from the already modified Metatheria. True, the 

 most useful and docile Hoofed Animals are looked 

 for in vain among the Marsupials, and notwith- 

 standing the great diversity in the formation of 

 their teeth which goes hand in hand with their 

 mode of life the types of the insect-, flesh-, grass- 



