202 
THE DESCENT OF MAN. 
Part I- 
of their successive appearance on the earth. The 
Lemuridse stand below and close to the Siraiadse, con- 
stituting a very distinct family of the Primates, or, 
according to Haekel, a distinct Order. This group is 
diversified and broken to an extraordinary degree, and 
includes many aberrant forms. It has, therefore, pro- 
bably suffered much extinction. Most of the remnants 
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 croivn 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 Simiadm were originally developed 
from the progenitors of the existing Lemuridse ; 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 r is. Hence the 
Placentata are generally supposed to have been derived 
from the I m placentata or Marsupials ; not, however, fro® 
forms closely like the existing Marsupials, but fro® 
their early progenitors. The Monotrcmata 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 Or®' 
thorhynchus and Echidna ; and these two forms may 
18 1 Man’s Place in Nature,’ p. 105. 
