LUMINESCENCE IN THE SEA 223 



by a protecting coat or capsule, and presenting, as in the 

 case of the higher Crustacea, a singular resemblance to the 

 structure of an eye. 



The cuttle-fish lights have generally been described as 

 blue, but in the case of the deep-sea Thaumatolampas diadema 

 most of the twenty-two organs scattered over the body 



Fig. 12. — Three specimens of Pholas ddctylus in their burrows, nat. size. 



show a white light, the two anal lights are ruby-red, a 

 median visceral light is ultramarine, and two ocular lights 

 are sky-blue. Whether all these different colours are pro" 

 duced in the cells from which the light emanates, or, as seems 

 more probable, are caused by some of the layers of tissue 

 through which the light passes to the exterior, is not yet 



