of the Arctic and the Antarctic Faunas. 311 



suflSciently cool water, since this quite agrees with the now 

 prevailing conditions of the subsurface- water fauna. 



We must accordingly expect to find in the oldest and 

 earlier middle Tertiary a large number of species identically 

 occurring in the northern and southern lieinisphere — for in- 

 stance, in our own region and in South Australia. If we 

 simply compare the lists that have been drawn up, this 

 certaiidy does not seem to be quite the case ; but if we take 

 account also of the remarks made by the authors, we find 

 that there is a large number of species closely allied to and 

 diflacult to distinguish from those of the Antipodes of a similar 

 age. When, further, we recall that the palaeontologists of 

 different countries have very often named their species with 

 little or no reference to the work of their colleagues, we 

 have to admit that the circumtropicity of the earlier Tertiary 

 faunas was so strongly marked that it extended not only 

 to the great majority of genera, but, in a great many cases 

 (whose number future studies will probably increase), even 

 to species. And thus it is certain that the Early Tertiary 

 fauna had an approximately similar uniform expression or 

 representation throughout the whole region of its distribution. 



"Universal" Faunas. 



The palaeontologists of the newer school are for the most 

 part strongly opposed to the theory of faunas of cosmopolitan 

 or universal character. Of course, if by a fauna of universally 

 or uniformly similar character any person means one which 

 exhibits in every locality throughout its region a similar 

 Combination of genera and species, he is asking more from 

 Nature than it is reasonable to expect, and neither zoologist 

 nor pala3ontologist can agree with him. We have, however, 

 on the earth at the present day two universal or unifornily 

 differentiated surface-water faunas which we know thoroughly 

 — the arctic and the tropical — and through these we can best 

 learn to recognize the characters of a uniformly different iated 

 or " universal " fauna. In the arctic fauna circumpolarity 

 is exhibited by a large percentage of species, and we get the 

 impression that it has hitherto been prevented in a consider- 

 able percentage more by some hindrance or other, and that 

 if all distribution-barriers were swept away circumpolarity, 

 and therefore universality, would reach the highest |)ossible 

 degree of develojjment within the arctic zone, ^vtn in the 

 arctic fauna, notwithstanding its pronounced circumpolarity 

 local differentiations have developed, and also local varieties 

 and races; but it seems quite certain that, if the local causes 



