200 i JOURNAL OF SCIENCE, 
It might have been expected that the Arctic Ocean would 
form a single province, and it might also perhaps have been 
expected that the south temperate zone would form a province 
divided into districts by the deep sea; but it could never have 
been expected that the animals of the North Pacific would 
prove to be so intimately allied to those of the North Atlantic 
that the two oceans would have to be united into one province. 
This is principally due to the resemblance between the marine 
faunas of Japan and of the Mediterranean, there being many 
identical species and genera found in both these districts, but 
which do not occur on either the Atlantic or the Pacific coasts 
of America. This proves that there must once have been a 
direct sea communication between the Mediterranean and Japan; 
and we learn from geology that an ocean, in which the “nummu- 
litic limestone” was deposited, did extend from Europe to 
China in the Eocene period. 
The tropical zone exhibits several peculiarities which could 
not have been predicted... The Indo-Pacific fauna is very homo- 
geneous and distinct ; its extension down the east coast of 
Africa is stopped by the cold current coming from the south- 
west that sweeps past Southern Africa; and very few Indo- 
Pacific forms have reached the Cape of Good Hope. But to 
the north this fauna pushes into the warm basin of the Red 
Sea; and, despite the Isthmus of Suez, it has invaded the 
Mediterranean, and even spread into the Atlantic—thus proving 
that the Isthmus of Suez must once have been submerged. To 
the eastward this fauna stops abruptly at the most easterly of 
the Polynesian Islands, not a single form apparently having 
crossed the deep ocean and reached America. The tropical 
American province is divided by the Isthmus of Panama, but 
this has comparatively little effect on the distribution of the 
animals, nearly one-half of the species being found on both 
sides. This fauna has pushed on to the Galapagos, and a few 
species have managed to reach the Sandwich Islands. The © 
Atlantic forms, however, have not travelled down to Peru, which — 
district is inhabited by the descendants of the aborigines that 
peopled the whole Pacific coast before the irruption of the 
Atlantic invaders. This proves that the Isthmus of Panama has 
been submerged at a not very remote period ; but as many of — 
the species have distinct varieties on each side of the Isthmus, 
the re elevation was evidently sufficiently long ago for a con- 
siderable amount of variation to have taken place subsequently : 
perhaps it occurred at the end of the Pliocene or beginning of 
the Pleistocene period. That the eruption was from the Atlantic 
into the Pacific, and that no migration took place in the oppo- 
site direction, was no doubt due to the great ocean current which 
now sweeps into the Gulf of Mexico, and is turned back as the 
Gulf Stream, at that time passing through into the Pacific 
Ocean. This diversion of the Gulf Stream probably helped to — 
produce the glacial epoch in Europe. ; 
Another remarkable peculiarity is the occurrence of the same — 
