My allusions to the lands lying beyond the Lusitanian province, refer chiefly to the Canary Islands and Madeira. Whatever doubts Dr. Wallace had on the subject of their former connection with Morocco, it cannot be denied that they used to be of much larger extent, especially in miocene and pliocene times. It seems extremely probable that these islands formed part of the mainland of North Africa until comparatively recently, and that they are the last traces of a sunken continent which united Africa and South America. A discussion of this problem, however, must be deferred, as it is a complicated one, and one which would lead me altogether outside the scope of this little volume. I hope I shall have an opportunity to publish my views on this subject before long, meanwhile the reader must content himself with this mere statement. During the greater portion of the Miocene, and I think for part of the Pliocene Epoch too, the advance of the Lusitanian species eastward was barred on the continent of Europe by an arm of the sea which stretched northward along the Rhone valley from the Mediterranean. The Lusitanian forms which originated in Southern Spain were able to travel east during these times by way of North-west Africa, Sicily, Southern Italy, and Greece; it is possible that some may have reached the Alps in this manner, and Eastern Europe generally. That the Lusitanian centre was never a very active one compared with, for instance, the Oriental is indicated by many distributional facts. It is difficult to understand, however, why the Oriental species, on the whole, have migrated so far west, while few Lusitanians have gone very far east. This seems to have been noted particularly in the case of the flora. Mr. Bonnet drew attention to the fact that in Tunis there are none of the absolutely characteristic plants of Morocco and Spain, while the Oriental flora is represented by a good many species. Lusitanian species have spread chiefly southward into North Africa, and northward into France, the British Islands, and even Scandinavia. As I have mentioned in the third chapter, there are a good many species of Lusitanian origin in the British Islands. However, we have only a mere remnant of what we ought to have, had the climate been less trying. It is probable, too, that the submergence destroyed a good many plants and the insects dependent on them. That the Lusitanian fauna is very ancient in the British Islands is proved by the fact of the discontinuous distribution of so many species. A greater number survived in Ireland than in England. [Illustration: Fig. 20.--The Strawberry-tree (_Arbutus unedo_) in its native habitat in the south-west of Ireland. (From a photograph by Robert Welch.)] [Illustration: Fig. 21.--The Irish Spurge (_Euphorbia hiberna_) in its native habitat in the south of Ireland. (From a photograph by Robert Welch.)]