would be no necessity for such an arrangement on the 
hypothesis of fixity of species ; but it is just what we 
should expect to find on the hypothesis of the transmu 
tation of species. Now, in this connection we venture to 
assert that there is no trace of the action of Natural 
Selection, but that, on the contrary, the principles of 
Natural Selection present great difficulties when we 
associate them with geographical distribution and the 
consequent transmutation of species. 
The cause of emigration is to be found in increase of 
numbers. Mr. Wallace says :— 
“Animals multiply so rapidly that we may consider them as con 
tinually trying to extend their range.”—(Geographical Distribution 
of Animals and Plants, vol. p. y.) 
But this assumption, that animals will always be trying 
to extend their range and that they will be forced to do 
so by continually increasing numbers, which make a given 
area a congested district so far as that species is con 
cerned, is not in accordance with the fact that, under 
ordinary occasions, the population of any species over a 
given area is uniform from generation to generation 
because the destruction is equal to the output of life. 
Nor does it seem to be generally true that animals 
manifest a universal readiness to migrate and to settle 
elsewhere. 
“The more permanent varieties are generally found, so far as 
I can discover, inhabiting distinct stations, such as high land or low 
land, dry or moist districts. Moreover in the case of animals which 
wander much about and cross freely, their varieties seem to be 
generally confined to distinct regions.”—(Origin of Species, p. i6ç.) 
“ Most animals and plants keep to their proper homes and do not 
needlessly wander about. We see this even with migratory birds, 
which almost always return to the same spot.”—(Origin of Species. 
A 72-)