292 THE MAMMALIA. 



existed in very early times, and had, at the begin- 

 ning of the Tertiary, already attained a stage of 

 development which has been transmitted to the 

 present members of the group, with but trifling 

 modifications; and it is probable that a transi- 

 tion into hoofed and carnivorous animals had 

 shown signs of incoming as early as the so-called 

 Mesozoic period. The question as to why all the 

 group did not join in the transformation is as 

 obvious as the answer to all similar questions : that 

 the special conditions of life for these animals 

 must have existed uninterruptedly, and that, in 

 addition, they possessed a great amount of adap- 

 tability. Thus we find the order of Insect-eaters 

 which is represented in Central Europe only by 

 the hedgehog, mole, and shrew, but more numer- 

 ously in other parts in many ways similarly 

 adapted to the most varied conditions of existence 

 as the Eodents. In fact, their variability, even in 

 primeval times, explains the fact of their having 

 been able to adapt themselves to entirely new 

 organisations, and Huxley specially traces to them 

 the hoofed and carnivorous animals. 



The same remarks apply to the Rodents, except 

 that in all of the periods known to us through 

 fossils, they were far more numerously represented. 



