THE DEEP-SEA FAUNA. 165 
owing to the fact that the temperature of the bottom continues | 
upward along the face of the ridges which separate the Carib- | 
bean from the Atlantic. 
While it cannot be denied that the littoral fauna is largely 
influenced by the fact that its inhabitants live within the limits 
of the action of the sun, — that is, in the variable limits of 
temperature (150 fathoms), — it does not follow that light 
alone, which perhaps does not penetrate even to one hundred 
fathoms, is the all-important factor regulating distribution. 
The action of the waves, of the shore currents, and of the 
tides, is only felt in that belt, and must exert a powerful influ- 
ence in modifying the habits of many of the littoral animals and 
plants. 
Species living beyond one hundred fathoms may dwell in total 
darkness, and be illuminated at times merely by the movements of 
abyssal fishes through the forests of phosphorescent aleyonarians, 
and by the feeble light which many of the deep-sea acalephs, 
echinoderms, and mollusks emit. Perhaps at those depths as 
beautiful effects may take place as attend the phosphorescence 
so common in shallow water along a coral reef. The structure 
of the organs of vision of the deep-water echinoderms, crus- 
tacea, polyps, mollusks, and annelids, differs only in a few cases 
from that of their congeners in shallower regions, to which the 
direct light of the sun penetrates. Were it not for the phos- 
phorescence, we might almost imagine the deep-sea animals 
devouring each other without ever having seen their food, and 
living for ages under conditions subject to but trifling changes, 
while during the same length of time terrestrial modifications of 
great importance were taking place. 
Many of the deep-sea gasteropods, as well as some of the 
fishes and crustacea, are blind. They belong generally to the 
more antique types, and the absence of eyes and the presence 
of rudimentary organs of sense are compensated by the de- 
velopment both in fishes and crustacea of tactile organs of 
gigantic size which serve as special organs of sense.' 
! Grimm, in studying the deep-water oped organs of sight, at the same depths 
fauna of the Caspian, notieed that, while there were genera in which the eyes are 
Several of the erustacea have well-devel- atrophied, and other organs of sense re- 
