38 — Geographical Distribution of. Crustacea. 
and species might readily be wafted to uncongenial climates, 
which would be their destruction ; in fact they could hardly es- 
cape this. Moreover, such seas are more boisterous than those 
nearer the equator. Again, these waters are almost entirely bare 
for very long distances, and not dotted closely with islands like 
the equatorial Pacific. 
In the northern hemisphere, on the eastern coasts especially, 
there are warm currents from the south and cold currents from 
the north. "'Tl'he former overlie the latter to a great extent in the 
summer and may aid southern species in northward migrations. 
Cape Hatteras is nearly the termination of the summer line of 
10? (see Maury's Chart), a temperature which belongs to the 
subtorrid region in winter. On the China coast, at Macao, there 
is a temperature of 83? in July, and in the Yellow Sea, of 78? 
to 809. But such northward migrations as are thus favored, are 
only for the season ; the cold currents of the winter months de- 
stroy all such adventurers, except the individuals of some hardier 
species that belong to the seas or have a wide range in distribu- 
tion. Sea-shore Crustacea are not in themselves migratory, and 
are thus unlike many species of fish. Even the swimming Por- 
tunidee are not known voluntarily to change their latitudes with 
. the season. 
'T'he following is a brief recapitulation of the more prominent 
facets bearing on these points. 
l. The distribution of individuals of many species through 
twelve thousand miles in the 'T'orrid zone of the Oriental seas. 
2. 'l'he very sparing distribution of Oriental species in Oecci- 
dental seas. 
2. 'The almost total absence of Oriental species from the west 
coast of America. 
A. 'The world-wide distribution within certain latitudes of the 
species we have called cosmopolites. 
5. The occurrence of closely allied genera at the Hawaiian. 
Islands aud in the Japan seas. 
6. 'The occurrence of the same subtorrid species at the Ha- 
waiin Islands and at Port Natal, South Africa, and not in the 
T'rrid zone intermediate, as Kraussia rugulosa and Galene na- 
talensis. 
7. 'The occurrence of identical species in the Japan seas and 
at Port Natal. 
8. 'The occurrence of the same species (Plagusia tomentosa) 
in South Africa, New Zealand, and Valparaiso ; and the occur- 
rence of a second species (Cancer Edwards ) ) at New Zeal- 
and and Valparaiso. 
9. 'l'he occurrence of closely allied species (as spaolés of Am- 
phoroidea and Ozius) in New South Wales and Chili. 
10. 'T'he occurrence of the same species in the Japan seas and 
the Mediterranean, and of several identical genera. 
.wX 
3 
