166 THREE CRUISES OF THE “ BLAKE.” 
A number of the deep-water species have retained habits of 
their congeners from shallower waters, which can be of little 
use to them. Far beyond the limits to which light is supposed 
to reach, we find’sea-urchins and ophiurans buried in the mud, 
like many of the littoral species. There are quite as many cases 
of mimicry among the ophiurans, polyps, crustacea, and annelids 
which cling to corals or polyps, and imitate their coloring, as in 
the littoral zone, under very dissimilar conditions of existence. 
As has been stated before, the deep-sea flora is most limited ; 
the more highly organized marine plants cannot, owing to ab- 
sence of light, flourish at any considerable depths. Dr. Car- 
penter dredged corallines in the Mediterranean at a depth of one 
hundred fathoms, and Dr. Duncan has noticed a parasitic fungus 
in corals from a depth of one thousand fathoms. He has also 
found a lowly organized substance, probably a plant, which bores 
into siliceous spicules. 
"The American land has occupied from the remote huronian 
period to the tertiary the same position as at present, the changes 
being merely those of relative level between land and sea. Dur- 
ing all these changes, there never has been a time when the land 
was not a fit resort for the leading forms of life, and the same 
is true of the ocean. We may imagine the distribution of land 
animals to have taken place from the arctic regions, and that 
they reached Australia, Africa, and South America, and there 
remained separated. The physical conditions of these regions 
were perhaps better adapted to the preservation of the types 
now characterizing them than to the production of new types. 
So may we imagine that from the Southern Ocean have little 
by little been sent forth the deep-sea forms which tend con- 
stantly to mix with the modified types farther north. 
That animal life could have been disseminated from the arctic 
regions as a centre can readily be conceived if we bear in mind, 
ceive a greater development; as in Ni- eyes, and the extraordinary development 
phargus, which has well-developed orgaus of tactile organs as special organs of 
of smell and of touch on its anteuns, sense. In Chologaster, another cave fish, 
while in Onesimus, with only rudimen- frequenting external waters of a subter- 
tary eyes, organs of touch are developed ranean origin, eyes are present, and tac- 
in its jaws. In Amblyopsis, from the tile organs are also developed. 
Mammoth Cave, we note the absence of 
