JOHN BUCK 761 



decapod shrimps (Fig. 9) and the crustacean compound eye (Fig. 10) . 

 There is, to be sure, no evidence that the rod-shaped individual 

 "photocyte" is a multicellular structure like the onmiatidium, though 

 Dcnncll (9) has shown that it has considerable complexity (Fig. 11), 

 nor that the photophore cornea is faceted (some compound eyes also 

 have a smooth cornea) . However, the resemblance to an eye in 

 general organ shape and in arrangement of luiits is certainly sufficiently 

 "frappant" (4) to explain their having beeii originally described as 

 eyes in the days before their light-emitting potentialities were known 

 (see Chim (4) for references) . 



In sinnmary, although there are clearly many photophores that 

 have only a specious structural similarity with actual eyes, it does not 

 seem possible to deny that some photophores do have a remarkable 

 resemblance. Further histological work is obviously needed, and 

 there is an e\en worse dearth of observations on the sovuxe of light- 

 emission, the physics of the ostensible dioptric structures, and the 

 nature of the beams emitted (divergent, collimated, or focused) . 

 However, it is really not necessary to debate the ultimate morphologi- 

 cal details of eye and photophore. It is enough to know that the 

 similarity is sufficiently compelling to have deceived professional 

 histologists into believing that both structures are eyes. Furthermore, 

 Ave could scarcely expect that eye and photogenic organ should have 

 identical structures if they have different functions. Actually, it is 

 practically impossible to make an objective evaluation of the struc- 

 tural interrelations apart from their evolutionary implications, which, 

 as we shall see, offer still more serious obstacles to acceptance. Even 

 so, and realizing the pitfalls of vicarious evidence, I confess to finding 

 the eye-photophore similarities, at least in the Crustacea, extraordi- 

 narily beguiling. Considering the abundance of available possible in- 

 tergrade structures (only a few of which have been touched upon) , 

 the differences in function, the differences in "host" structure and 

 habit, and the presumably ancient origin of both types of organ, it 

 seems almost inconceivable that entirely independent structures could 

 by accident be so similar. However, it has to be admitted that two 

 of the original investigators who actually worked on the material, 

 albeit apparently without knowledge of decapod photophores, con- 

 cluded that the schizopod photophore (Fig. 3) is an organ sui generis 

 (4, 26). 



At this point, if not before, the skeptic will quite properly ask 

 whether it is really certain that these eye-like organs produce light. 

 If he knows, in addition, that most of the photophores and eyes re- 



