256 MARINE ANIMALS 



light-producing insects. Light production may nevertheless be said to 

 be especially characteristic of the deep-sea animals. 



The production of light by animals of the littoral benthos is excep- 

 tional (Pholas) ; in the abyssal the bottom swarms with light producers. 

 The largest number is perhaps supplied by the alcyonarian coelen- 

 terates — Alcyonidae, Pennatulidae and Gorgonidae. The echinoderms 

 have the starfish Brisinga and Freyella, and the annelids are repre- 

 sented by Chaetopterus and Polynoe. All these have usually a con- 

 tinuous light, whose clarity and beauty of color delight every observer. 

 De Folin 15 expresses his impressions of nocturnal dredging as follows: 

 "How great was our astonishment when a great number of bouquet- 

 like gorgonids were taken from the net; these sent forth flashes of 

 light so bright that the 20 torches lighting the work paled into insig- 

 nificance as soon as the polyps were near them. From every point of 

 the main stems and branches beams of light radiated, whose intensity 

 became less, then increased, passing from violet to purple, from red 

 to orange, from blue to various tones of green, and sometimes to the 

 white of flowing iron. Meanwhile the predominant color was plainly 

 green, the others appearing momentarily and melting quickly into the 

 general color." In all these animals the power of light production is 

 not confined to special organs, but is more or less diffused over the 

 body. 



Bioluminescence is even more frequent among the abyssal pelagic 

 forms. No less than 44% of the fishes of depths beyond 900 m. are 

 light producers. 16 By direct observation, Beebe 5 found the first animal 

 lights at 207 in. and thereafter in slowly increasing numbers down to 

 the greatest depth reached, 924 m. Diffuse luminescence occurs among 

 the macrurids, which give off light-producing mucus from their skin 

 glands. For the most part, however, the pelagic forms have special 

 luminescent organs, which are under the control of the nervous system. 

 In some forms these organs are simple in structure and are mere ac- 

 cumulations of gland cells with a luminescent secretion. In other groups 

 the structure becomes more complex and reaches its highest degree 

 among the Euphausidae (Crustacea), the cephalopods, and the bony 

 fishes. Convergence in the evolution of these organs in such diverse 

 groups is notable. Behind the group of light-producing cells is located 

 a tapetum, in the form of a concave reflector, covered over by a pig- 

 ment layer. An outer lens is present, formed in different ways in the 

 different animals (Fig. 67). Independent convergent origin of light 

 organs may be seen even among the different cephalopods and fishes. 

 It is notable that light production is absent among the cephalopods and 

 fishes of shallow water. The deep-sea members of the Iniomi (lantern 





