308 THREE CRUISES OF THE “ BLAKE.” 
ing the vision of marine animals, and we should be careful in 
drawing conclusions with reference to physical conditions de- 
rived from the functions of organs of sense, which may serve 
other purposes than those of vision alone. The sense organs 
of coelenterates and of annelids, varying between mere pigment 
spots and more complicated organs, may be of use, not only to | 
detect differences in the intensity of light, but also in receiving 
other impressions, — of sound, motion, or heat. 
The deep-water gasteropods, with rudimentary eyes, or to- 
tally blind, live as do their littoral congeners, buried in mud. 
The blind fishes belong to families with burrowing habits, 
and living in the soft deep-sea mud. Their organs of vision 
may gradually have become atrophied, and been replaced by 
highly specialized tactile organs. The same thing occurs with 
crustacea. Astacus zaleucus is blind, its claws are long and 
delicate, and with similar tactile organs must be of assistance 
to them in enabling them to feel their way about. Dr. 
Carpenter and Professor Thomson came to the conclusion 
that phosphorescent animals play an important part in lighting 
up the abyssal regions of the sea. "The contents of the trawl 
are frequently brilliantly phosphorescent, and among the deni- 
zens of the deeper regions are a number of highly luminous 
anthozoa, ophiurans, hydroids, crustacea, and even fishes. 
Swimming or creeping between the forests of gorgonians,! 
which become luminous by disturbances due to currents or other 
movements, the deep-sea crustacea, fishes, cephalopods, echino- 
derms, and others, must be able to see a considerable distance 
during the emission of the phosphorescent light, and thus re- 
ceive assistance in searching for their food. The light devel- 
oped from such a source, and in such a manner, cannot be | 
very intense, and yet such areas may be, as has been stated | 
by Moseley, favorite spots where deep-sea animals congregate. 
It has been suggested by Professor Verrill that this phos- | 
phorescence is protective, and may prevent fishes and other 
animals from browsing on the luminous actinozoa, lest they 
1 Such forests we find commonly on stance, where the masses of animals ac- 
the shallower slopes of the continental cumulated within quite limited areas are 
areas, as on the Florida plateau for in- really prodigious. 
