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 Hghts 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 



Fia. 12. — Three specimens of Pholaa dactylua in their burrows, nat. size. 



show a white Hght, the two anal Hghts are ruby-red, a 

 median visceral Hght is ultramarine, and two ocular Hghts 

 are sky-blue. Whether aU these different colours are pro- 

 duced in the ceUs from which the Hght emanates, or, as seems 

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

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



