Many other naturalists have worked in the direction I have indicated--namely, in grouping the British animals into several distinct assemblages, without, however, taking their foreign range into consideration, or their origin. I have already referred to the useful work done by botanists, who have been the pioneers in the science of the geographical distribution of living organisms. Among the British naturalists who have applied the principles of Watson to zoology, A. G. More deserves to be specially mentioned. He was the first to make a serious study of the British fauna on the lines laid down by that distinguished botanist. In conjunction with E. Boyd, he published a valuable essay on the "Distribution of Butterflies in Great Britain," and later on the birds were similarly dealt with. All the more important groups of animals are now being studied with a view to determining their exact range in these islands. Mr. Harvie-Brown, Mr. J. W. Taylor, Mr. Eagle Clarke, Mr. Miller Christy, Mr. Ussher, Mr. Barrington, and a number of others have considerably advanced our knowledge in this direction in recent years. Any such contributions are to be welcomed as furnishing us with the necessary data to solve the problem of the origin of the British fauna. Meanwhile we know enough to enable us to assert positively that the latter has reached us by land-connections from various parts of Europe (cf. p. 35). This statement of course refers to the bulk of the British fauna. The small proportion of indigenous species, or such as have been introduced accidentally, may be left out of consideration when dealing with the great mass of animals which have evidently migrated to the British Islands on land now sunk beneath the sea (see Fig. 4, p. 60). Opinions of zoologists, botanists, and geologists are practically unanimous on this subject; yet there are two other theories, which have from time to time been advanced to account for the origin of the British fauna. Only the first of these, however, can claim the serious attention of those interested in the problem. Its chief contention lies in the oft-asserted dictum of the "_imperfection of geological record_." It has been suggested, in fact, that the British fauna, instead of having migrated to our islands, might have originated there, but that, owing to the fragmentary nature of our Tertiary deposits, all trace of their early history had disappeared. "The origin of European species," remarks Professor Cole (p. 238), "within the area of the British Isles, and their migration outwards when local conditions became less favourable for their multiplication, are possibilities that seem too often disregarded. Yet the geologist must see in the western borderland of modern Europe a diminished continent from which land-animals must have again and again moved eastward." "Hence geologists may fairly be unwilling to look on our isles as barren lands waiting to be peopled in pliocene or later times.