In the sixth chapter I enumerated the chief objections which might be justly urged against the views maintained in this volume.

Most of them have now been discussed.

One, namely, the distinctness of specific forms and their not being blended together by innumerable transitional links, is a very obvious difficulty.

I assigned reasons why such links do not commonly occur at the present day under the circumstances apparently most favourable for their presence, namely, on an extensive and continuous area with graduated physical conditions.