difference than that between the local forms and sub-species, they are almost universally ranked by naturalists as true species.

Nevertheless, no certain criterion can possibly be given by which variable forms, local forms, sub species and representative species can be recognised.

Many years ago, when comparing, and seeing others compare, the birds from the closely neighbouring islands of the Galapagos Archipelago, one with another, and with those from the American mainland, I was much struck how entirely vague and arbitrary is the distinction between species and varieties. On the islets of the little Madeira group there are many insects which are characterized as varieties in Mr. Wollaston’s admirable work, but which would certainly be ranked as distinct species by many