JOHN BUCK 765 



tones of teleology it will be assumed that the observed photophore 

 structures and interrelations have usefulness to the organism. In this 

 connection it may be instructive to summarize briefly the sorts of uses 

 for photophores that have been suggested in a variety of animals. 



In view of the spectacular nature of bioluminescence it is almost 

 unbelievable that its utility to the organism has not been unequi- 

 \ocally established, either observationally or experimentally, except 

 in the single instance of the mating signals of the firefly. A similar 

 function has been guessed at in the Japanese hotaru-ika, or "firefly 

 squid," but it is clear that the rarity and extreme delicacy of these 

 and other bathypelagic organisms will make direct observation of 

 luminescent behavior under natural conditions very difficult. The 

 suggested fishing lure utility of the barbel organs of the angler fishes 

 is a similarly reasonable but speculative use for the organisms under 

 consideration. Other functions, such as protection by signifying un- 

 palatability or by frightening off predators, or as a "burglar alarm" 

 (2) in which the victim's signal enables other members of the species 

 to escape, seem still more hypothetical. Chun (4) claimed that the 

 schizopod thoracic and abdominal photophores are aimed ventrally 

 and laterally and he apparently thought that the resulting illumina- 

 tion would somehow aid, in conjunction wath specialization of the 

 ventrolateral regions of the compound eye, the handling of prey caught 

 by the thoracic appendages (an operation done by "feeling" by most 

 Crustacea) . One unexplained attribute of many of the shrimp photo- 

 phores is that they are apparently movable, by specific muscles (e.g., 



4,9). 



In regard to deep-sea squids and shrimps we may perhaps focus 

 special attention on the facts that these creatures normally live for 

 long periods in an environment of perpetual and complete absence 

 of daylight, and that they have well-developed eyes. It would there- 

 fore seem reasonable that one function of light-production could be 

 in providing recognition signs to keep members of the school from 

 straying apart forever into the vast and trackless depths. In animals 

 breeding by sexual contact, some such mechanism for promoting 

 gregariousness would seem to be essential for the continuation of the 

 species. In addition, since both groups are amply well-developed, 

 neurally, there appears to be no reason why species-specific mating 

 signals could not develop for use during their reported diurnal or 

 seasonal migrations to the surface at night for breeding. Dennell (10) 

 and especially Nicol (24) have made some interesting estimates of the 

 distance that light from deep-sea shrimps might be visible to another 



