THE GLACIAL RANGE CONTRACTION, ETC. 167 



area affected/ save, of course, in such instances which 

 purely apply to Inter-polar or Inter-hemisphere species. 

 Of course it does not come within our present pro- 

 vince to seek to show how Evolution progressed, and 

 the segregation of species went on throughout this 

 awful era, but that it was a means of much differenti- 

 ation is unquestionable. 



^ I may here take the opportunity of pointing out that of the 

 three small families of birds that have solely survived the Ice Age 

 in the Nearctic and Paleearctic regions (the Alcida;, Colymbidae, and 

 Panuridce), by far the most extensive group — the Alcida; or Auks — - 

 numbering some thirty species survives in greatest abundance in 

 the region luhefe glacial conditions were the least pronounced ! This 

 family of birds may be said to have its head-quarters now round 

 the coasts of the North Pacific (from California to Japan), where 

 not only the bulk of the species are found, but where it preserves 

 the greatest diversity of its surviving development. There can be 

 little doubt that before the Glacial Epoch the Alcidai were a large 

 circumpolar family ; during that era they suffered almost complete 

 extermination, the only survivors being those species or their 

 ancestral forms whose breeding range extended beyond the adverse 

 influences associated with that period. By far their most important 

 range base during the Ice Age must have been the Asiatic coasts 

 and islands of the North Pacific, and possibly the Aleutian Islands 

 — areas, be it remarked, that remained for the most part free from 

 glaciation. A few species, as we have already noted, survived in 

 the North Atlantic, owing partly, as we have abundant evidence to 

 suggest, to the fact of their pre-glacial breeding range, or a portion 

 thereof in the east, having been in the area I have designated 

 Range Base I. {con/, pp. 6S-77). 



