194 THE DESCENT OF MAN. [Part I 



Blight aid from the periods, as far as ascertained, of their 

 successive appearance on the earth. The Lemuridse stand 

 below and close to the Sirniadse, constituting a very dis- 

 tinct family of the Primates, or, according to Hackel, a 

 distinct Order. This group is diversified and broken to 

 an extraordinary degree, and includes many aberrant 

 forms. It has, therefore, probably suffered much extinc- 

 tion. Most of the remnants survive on islands, namely, iu 

 Madagascar and in the islands of the Malayan archipelago, 

 where they have not been exposed to such severe compe- 

 tition as they would have been on well-stocked continents. 

 This group likewise presents many gradations, leading, as 

 Huxley remarks, 18 " insensibly from the crown and sum- 

 mit of the animal creation down to creatures from which 

 there is but a step, as it seems, to the lowest, smallest, 

 and least intelligent of the placental mammalia." From 

 these various considerations it is probable that the Simiadae 

 were originally developed from the progenitors of the ex- 

 isting Lemuridse ; and these in their turn from forms stand- 

 ing very low in the mammalian series. 



The Marsupials stand in many important characters 

 below the placental mammals. They appeared at an 

 earlier geological period, and their range was formerly 

 much more extensive than what it now is. Hence the 

 Placentata are generally supposed to have been derived 

 from the Implacentata or Marsupials ; not, however, from 

 forms closely like the existing Marsupials, but from their 

 early progenitors. The Monotremata are plainly allied to 

 the Marsupials ; forming a third and still lower division in 

 the great mammalian series. They are represented at the 

 present day solely by the Ornithorhynchus and Echidna ; 

 and these two forms may be safely considered as relics of 

 a much larger group which have been preserved in Austra- 

 lia through some favorable concurrence of circumstances. 



18 ' Man's Place in Nature,' p. 105. 



