356 Geographical Distribution of Crustacea. 
ern species, and each of these localities is within the subtemper- 
ate region. We are not ready however to assert, that such j jour- 
neys as this range of migration implies are possible. The oceanic 
currents of this.region are in the right direction to carry the spe- 
cies eastward, except that there is no passage into this western 
current from Cape Horn, through the Lagulhas current, which 
could have survived the boisterons passage, and finally have “he 
a safe landing on the foreign shore. The distance from 
Zealand to South America is five thousand miles, and there is iat 
‘present not an island between 
VI. Part of the difficulty in ) the way of a transfer of species 
between distant meridians might be overcome, if we could as- 
sume that the intermediate seas had been occupied ~ yer or 
islands during any part of the recent epoch. In the case eae 
alluded to, it is possible that such a chain of interrupted co 
nication once had place; and this bare possibility reskele np 
force of the argument used above against migration. Yet as 
is wholly an assumption, we cannot rely upon it for ileal 
that migration has actually taken place, 
Vil. The existence of the same species on the east and west 
coasts of America, affords another problem, which migration can- 
not meet, without sinking the isthmus of Darien or Central 
America, 'to afford a e across. We know of no evidence 
whatever that this portion of the continent has pe beneath the 
ocean during the recent epoch. An argument against such a sup- 
position might be drawn from the very small number of species 
that are identical on the two sides, and the character of these spe- 
cies. Libinia spinosa occurs at Brazil — a and has not 
been found in the West Indies. Leptopodia sagittaria, another 
vai occurs at Valparaiso, the West Indies, and the Canaries. 
that in all instances the distribution here is owing to migration; 
nor will it be admitted unless other facts throw the weight of 
probability on that side. 
IX. But when we find the same Temperate zone species oc- 
curring in distant provinces, these provinces having between 
them no water communication except through the Torrid or 
a zone, —n offering no ground for the supposition that 
. on has existed during the recent epoch, we are are led 
