534 THE POPULAR SCIENCE MONTHLY 



duction of a sound would be better so far as transmission is concerned, 

 for water is an excellent transmitter of sound ; but to produce a sound, 

 especially under water, a not inconsiderable amount of power is re- 

 quired — as may easily be demonstrated by trying to clap one's bands 

 under water — and tbis amount of power is far and away beyond any 

 possessed by tbe luminous marine creatures. True, some fish emit 

 sounds — e. g., the drum-fish — but those marine creatures which do so 

 are of considerable power and a quite high degree of organization. All 

 living creatures, probably without exception, produce a certain amount 

 of heat through their life-processes; but heat is obviously of no value 

 so far as the purposes of communication are concerned, especially in 

 an immense body of liquid of high specific heat. Variations in pressure 

 more especially vibrations of longer interval than those of sound, may, 

 of course, be produced and transmitted very effectively, but here again 

 much power is required. As a matter of fact, some species of fishes 

 have been found to possess along their lateral line, organs susceptible 

 to vibration-frequencies approaching six per second in the water. Elec- 

 tricity is a possibility, but in all cases of electrical tissues so far studied, 

 considerable masses of muscular tissue have been found as the site of 

 the electrogenic phenomena, again a matter out of the question for a 

 simple organism. With light the problem is different : All that is neces- 

 sary is the elaboration by the cell through its vital processes of a sub- 

 stance which, when in contact with the oxygen dissolved in the sea- 

 water, will produce light. Since certain bacteria can produce such a ma- 

 terial from a compound as comparatively simple as asparagin (amino- 

 suecinamidic acid, CONH 2 -CHNH 2 -CH 2 -C0 2 H), this is a matter of 

 comparative ease and requiring nothing more than the metabolic proc- 

 esses which might be ordinarily expected. After synthesis, the sub- 

 stance when brought into contact with the sea-water would be oxidized 

 with the evolution of light. Light knows little of water currents, and 

 but little more of differences in concentration; it would spread in all 

 directions from the point of emission, and to the delicate structures of 

 the ocean fauna and flora, would, however weak it might appear to hu- 

 man eyes, be sensible for considerable distances. Hence light is an 

 ideal method of communication for marine forms of low organization 

 and indeed for many of those of higher organization. 



Returning again to a discussion of the various forms : Perhaps the 

 first case, in the upward scale, where we may apply with any degree of 

 certainty one of the uses mentioned before, is that of certain marine 

 worms, the Annelids. Professor W. T. Galloway has recentky shown 

 the use of photogenicity in a species of Odontosyllid as a mating 

 adaptation, with evidence which leaves little ground for doubt. In this 

 case propagation of the species appears to be entirely dependent upon 

 a periodic photogenicity limited to certain more or less definite por- 



