JOHN BUCK 767 



elusion that eye-like photophores are limited to inhabitants of deep 

 waters. In view of the virtual absence of photophores among tetra- 

 branch cephalopod molluscs (i.e., the planktonic nautiloids) and 

 octopods (the characteristically shallow-water cuttlefishes) , it is also 

 tempting to see confirmation of the idea that bioluminescence must 

 develop before eyed forms can venture permanently into stygian 

 depths. However, not enough is known about squids (1, 6) to tell 

 whether the oegopsids, with their good eyes and good photophores, 

 have a characteristically deeper habitat than the myopsids, with their 

 also excellent eyes but absent photophores. 



The squids Histioteuthys and Calliteuthys present a different type 

 of puzzle, in that both species have enormously developed left eyes, 

 bearing mostly rudimentary photophores, while the smaller right eyes 

 bear a circlet of well-developed photophores (6) . 



Another eye-photophore interrelation that has been suggested (11), 

 and which is perhaps not outrageously more speculative than some of 

 the preceding, is that an organ might function simultaneously as eye 

 and photophore. Incoming light could then serve to excite the photo- 

 genic tissue directly and the dual organ could serve as a local-reflex 

 signalling device. This would at least make it easier to understand 

 the presence of ostensible collimating structures in photophores, both 

 functionally and with respect to evolution. 



A third possibility, that high hydrostatic pressure is a photophore- 

 inducer, has thus far not been possible to test, for lack of permanently 

 dark, but shallow, marine habitats. Cave-dwelling fauna, whether eyed 

 or blind, consistently lack photophores; but the significance of this 

 otherwise arresting fact is vitiated by another and overriding peculi- 

 arity of bioluminescence, namely, that it is essentially absent in 

 freshwater forms. 



Summation 

 It has to be admitted that the number of old mysteries concerning 

 bioluminescence has not been reduced by redescribing them, though 

 benefit may eventually come simply from thus exposing them to 

 a new generation of biologists, physicists, and chemists. For example, 

 in spite of Wald's well-taken point that photosynthesis is actually 

 closer to bioluminescence than is vision, I think it would not be amiss 

 if biochemists stayed alert to possibilities of kinship between light 

 production and light absorption. We surely have enough examples 

 of swapped, shared, and made over molecular types and enzymatic 



