308 THREE CRUISES OF THE " BLAKE." 



iiiof the vision of marine animals, and we shonld be careful in 

 drawing conclusions with reference to j^hysical conditions de- 

 rived from the functions of organs of sense, which may serve 

 other purposes than those of vision alone. The sense organs 

 of coeleuterates and of annehds, varying between mere pigment 

 sjjots and more complicated organs, may be of use, not only to 

 detect differences in the intensity of light, but also in recei\ing 

 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 may gradually have become atrophied, and been replaced by 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. Asfacus 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 ti-awl 

 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, ceplialopods, echino- 

 derms, and others, must be able to see a considerable distance 

 during the emission of the phosj)liorescent 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 ou stance, where the masses of animals ac- 

 the shallower slopes of the continental cunmlated within quite limited areas are 

 areas, as on the Florida plateau for in- really prodigious. 



