THE animal life or fauna of a country is no fixed unit of occupation, established and unchanging, but, endowed with the plasticity of life, it carries in itself the imprints of many influences which have played upon it throughout the ages.

The lectures contained in the following pages were planned to unravel one important set of such influences those which radiate from the acts of Man so that it might be possible to trace the different ways in which Mans power has worked and is working, and to realize to what degree a fauna of to-day owes its character and composition to his interference.

With this end in view it was necessary to select a particular fauna of manageable compass, where the inquisition into Mans influence could be pushed to the furthest limits ; and several facts pointed to the fauna of Scotland as best suited for the purpose.

Nevertheless, I have not hesitated to refer to examples of Mans influence in other countries, wherever particular types have been strikingly illustrated, or where influences are seen at work which help to explain effects of causes long lost to sight in Scotland, or where, as in the case of counter-pests, modern science has created new kinds of interference which sooner or later are likely to be adopted in this country.

A result of this enquiry has been to emphasize the in- stability and changefulness of a fauna, and a word may be said as to the general place of Mans influence in the sum of change.