Of these three essential factors, space might be said to be one with which biogeography is primarily concerned. However space necessarily interplays with time and form, therefore the three factors are as one of biogeographic concern.

Let us suppose that we have laid on the table... [a] piece of glass... and let us homologize this glass to a whole order of plants or birds. Let us hit this glass a blow in such a manner as but to crack it up. The sectors circumscribed by cracks following the first blow may here be understood to represent families. Continuing, we may crack the glass into genera, species and subspecies to the point of finally having the upper right hand corner a piece about 4 inches square representing a sub-species.

I have indeed lived and worked to my taste either in art or science. What more could a man desire? Knowledge has always been my goal. There is much that I shall leave behind undone...but something at least I was privileged to leave for the world to use, if it so intends...As the Latin poet said I will leave the table of the living like a guest who has eaten his fill. Yes, if I had another life to spend, I certainly would not waste it. But that cannot be, so why complain?

Of these three essential factors, space might be said to be one with which biogeography is primarily concerned. However space necessarily interplays with time and form, therefore the three factors are as one of biogeographic concern.