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 Hght 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- 

 inor- all these chano^es, there never has been a time when the laud 

 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 organs of tactile organs as special organs of 



of smell and of tonch on its antennje, sense. In Chologaster, another cave fish, 



while in Onesimus, with only riidimen- freqnenting 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 



