760 LIGHT AND LIFE 



related, in other words, we should not expect that modern photophore 

 and modern eye will necessarily correspond in all structural details. 

 This is fortunate, incidentally, since I found no instance where ocellar 

 structure and photophore structure have both been studied in the 

 same species. This has made it necessary sometimes to compare only 

 distantly related forms that might be expected to differ somewhat 

 merely as a consequence of one being terrestrial and another aquatic, 

 or because of one respiring via tracheae and another via blood gills. 



Referring now to specific examples, there seem to be three some- 

 what different structural parallels between crustacean photophores 

 and arthropod eyes. The first, exemplified by the thoracic photo- 

 phores of schizopod shrimps (Fig. 3) , has several unusual and charac- 

 teristic structural features, all of which have counterparts in various 

 arthropod eyes. For example, the thick hemispherical reflector which 

 makes it necessary for the nerve supply to enter from the side, is al- 

 most exactly matched by the tapetum and nerve arrangement of the 

 pseudoscorpions and pedipalps (Fig. 4) . The refractor, likewise, 

 has its counterpart in modifications of the sublenticular or "cornea- 

 genous" portion of the insect ocellar hypodermis into striated refractile 

 structures, the "Stabchen" of the unit eye of Xeyios (RFR, Fig. 5) or 

 in the "Glaskorper" of many ocelli (RFR, Fig. 6) . The separate lens 

 itself seems more similar to the internal "crystalline lens" of a larval 

 insect stemma than to the separate multicellular lens of forms like 

 Cloeon (see Hesse, (16), Fig. 15). The curious lamellated ring ("ex- 

 ternal reflector" of Trojan, 28)3 ^as shown by Chun (4) to be a 

 derivative of an hypertrophied region of the hypodermis which is 

 found in the somewhat simpler (lensless) eyestalk photophores of the 

 same shrimps (see Chun's Fig. 1). This region in turn is paralleled 

 by a common insect ocellar structure (the "iris" of Redikorzew (25) , 



Fig. 6) . 



The second type of photophore, the eyestalk organs of decapod 

 shrimps (Figs. 7, 10), most resemble, among eyes available for com- 

 parison, the ocelli of insects, although it is difficult to match all 

 structural features in one ocellus. Perhaps the best fits are the ocelli 

 of a butterfly (Fig. 8) and a wasp (Fig. 6) . Pigment cup and tapetum 

 seem to be lacking in both, but are present in many other ocelli (e.g., 

 Cloeon, Ceratopsyllis and Agrion — Hesse's (16) Figs. 15, 17, 26). 



The most convincing — or perhaps most meretricious — eye-photo- 

 phore similarity is between the organs found on the leg bases of many 



=» Physicists who have gotten into the spirit of this inquiry will recognize the 

 similarity to a Fresnel lens. 



