I quite feel the comfort of writing when one may "alter one's speculations the day after." It is beyond my knowledge to weigh ranks of birds and monotremes; in the respiratory and circulatory system and muscular energy I believe birds are ahead of all mammals.
I knew that you must have known about New Guinea; but in writing to you I never make myself civil! After treating some half-dozen or dozen domestic animals in the same manner as I treat dogs, I intended to have a chapter of conclusions.
But Heaven knows when I shall finish: I get on very slowly.

You would be surprised how long it took me to pick out what seemed useful about dogs out of multitudes of details.
I see the force of your remark about more isolated races of man in old times, and therefore more in number.

It seems to me difficult to weigh probabilities.

Perhaps so, if you refer to very slight differences in the races: to make great differences much time would be required, and then, even at the earliest period I should have expected one race to have spread, conquered, and exterminated the others.
With respect to Falconer's series of Elephants (112/5.

In 1837 Dr.
Falconer and Sir Proby Cautley collected a large number of fossil remains from the Siwalik Hills.