ia6 THE LIFE OF CRUSTACEA 



lustre. Before their luminosity was observed, these 

 organs were described as " accessory eyes," but there 

 can be little doubt that they serve rather as search- 

 lights, although, from the positions that some of 

 them occupy on the body, it is not easy to see how 

 they can illuminate objects within range of the eyes. 

 That the function of phosphorescent organs is not 

 always that of giving light for their possessor to see 

 by is shown by the fact that many luminous animals 

 are blind. It is important to notice, however, that 

 these blind animals never have complex " photo- 

 phores" like those just described, but only exhibit 

 a diffuse luminosity or give off luminous secretions ; 

 as an example among Crustacea, the blind Eryonidea 

 (see Fig. 46, p. 133) may be mentioned, one species of 

 which was observed by Alcock to be "luminous at 

 two points between the last pair of thoracic legs, 

 where there is a triangular glandular patch." In a 

 recent discussion of the whole question of phos- 

 phorescence in marine organisms, Dr. Doflein con- 

 cludes that the part it plays in the life of the 

 animal probably differs in the different cases. In 

 some it may serve to attract prey, as moths are 

 attracted to a candle ; in others it may help 

 individuals of the same species to keep together 

 in a swarm or to find their mates, the varying 

 arrangement of the photophores producing character- 

 istic light-patterns that serve as " recognition marks " 

 like the colour-patterns of animals that live in the 



