740 THE EYE IN EVOLUTION 



The Arthropods contain many luminous species, most of them Crus- 

 taceans and Insects, a few of them Myriapods and Arachnids. Luminescence 

 among Crustaceans is seen at its best in Copepods and Ostracods while the 

 brilliantly luminous shrimps, Meganyctiphanes, as they rise in immense 

 shoals with the cold currents from the depths of the sea, glitter with 

 millions of pin-points of light as they surface over a wide area. Several species 

 of deep-sea Crustaceans have luminous organs, one of peculiar interest 

 appearing anatomically as a segment of a composite compound eye {Stylo- 

 cheiron mastigophoruvn — Chun, 1896).i Only in a few orders of Insects are 

 luminescent types found such as the Collembola (springtails), the Hemiptera 

 (lantern flies) and the Diptera (fungus-gnat larvae), but the most striking 

 examples are found among the beetles (Coleoptera) particularly the Lampy- 

 rids and Elaterids {Lampyris noctiluca, Photinus pyralis, etc.) (Figs. 889-90) ; 



Fig. 891. — LrcoTECTHit! diadema as it might look in the Deep Sea (after 

 Dahlgren, from a drawing by Bruce Horsfall ; E. N. Harvey's Biolutninescence, 

 Academic Press). 



the fascination of the signalling of the winged male fire-fly (or more correctly 

 fire-beetle) to his wingless mate, the glow-worm, or the beauty of the 

 rhythmic synchronous flashing of a cloud of fire-flies in a tropical evening 

 has long attracted attention (Buck 1937-47) (Figs. 893 and 894). 2 



Several Molluscs are luminescent, some such as the bivalve, PJiolas, 

 having glandular organs in the siphon which secrete a luminous slime, while in 

 others such as the nudibranch, Phyllirrhoe (the "flowing leaf" of the 

 Mediterranean and Atlantic), they are distributed over the whole body 

 (Trojan, 1910). The most conspicuous examples, however, are found among 

 Cephalopods,^ about half the species of which emit light. So elaborate may 

 the mechanism in these creatures become that up to four different colours of 

 light are produced by the highly specialized luminous organs in certain 

 deep-sea squids in the Pacific Ocean (the " wonder lamp " Lycoteuthis — 

 Okada et al, 1933 ; Takagi, 1933) (Fig. 891). 



Among the Protochordates, some species of Hemichordates luminesce 

 such as the balanoglossid, Ptychodera (Crozier, 1920), as well as certain 

 colonial Tunicates such as the beautiful Pyrosoma: a whole colony of 

 the latter with its numerous individuals swims as one creature and if 



1 p. 160. 2 p_ 58^ 



^ For review, see Berry (1920). 



