Bae 
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: 
7 aH 
Geographical Distribution of Crustacea. . B53 
characteristics as species depend. ‘These characteristics are of 
no climatal origin. They are the impress of the Creator’s hand, 
when the species had their first existence in those regions calcu- 
lated to respond to their necessities. 
The following questions come up under this general head :— 
1. Have there been local centres of creation, from which 
groups of species have gone forth by migration? 
2. Have genera only and not species, or have species, been re- 
peated by creation in distinct and distant regions? 
ow closely may we recognise in climatal and other physi- 
cal conditions, the predisposing cause of the existence of specific 
more generally diffused. ; 
A direction and also a limit to this migration exist, (1) in the 
currents of the ocean, and (2) in the temperature of its different 
regions. Through the Torrid zone, the currents flow mainly 
from the east towards the west; yet they are reversed In some 
parts during a certain portion of the year. But this reversed eur- 
rent in the Pacific never reaches the American continent, and 
hence it could never promote migration to its:shores. 
y 
the middle and higher temperate regions. But the temperature 
regions in these latitudes are more numerous than in the tropics, 
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 t 
nearer the equator. Again, these waters are almost entirely bare 
for very long distances, and not dotted closely with islands like 
70 
subtorrid region in winter. On the China coast, at Macao, there 
Secoyp Seeies, Vol. XX, No. 60.—Nov., 1855. 45 
