202 THE DESCENT OF MAN. Part I. 



of their successive appearance on the earth. The 

 LemuridsB stand below and close to the Simiadae, con- 

 stituting a very distinct 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, pro- 

 bablv suffered much extinction. Most of the remnants 



at 



survive on islands, namely in Madagascar and in the 

 islands of the Malayan archipelago, where they have 

 not been exposed to such severe competition 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 

 " summit 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 existing Lemuriclae ; and 

 these in their turn from forms standing 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 Orni- 

 thorhynchus an r l Echidna ; and these two forms may 



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



