PHOTOGENIC MARINE ANIMALS. 13 



other hand, thinks they have. Flashes of light proceed from 

 these organs, and when dying the whole body is frequently 

 diffusely luminous. Similar organs are found in Nyctiphanes 

 norvegica, the phosphorescence of which was observed by Sars, 

 and afterwards by G. J. Murray, in the Faroe Channel. This 

 species often appears in vast numbers on the east and west 

 sands, St. Andrews, where their stranded multitudes resemble 

 chaff, and along with them is Thysanoessa, the luminous globules 

 of which agree in structure with the foregoing. 



In certain crustaceans (Leucifer, Aristceus, and probably in 

 Munida and Dorynchus) the eyes are brilliantly phosphorescent. 

 In species of Aristceus, Heterocarpus, and Pentacheles, recently 

 dredged by Dr. Alcock* off the Andaman Islands, luminosity 

 also occurred. In the two former the light appeared to come as 

 a secretion near the openings of the green glands. Heterocarpus 

 (both male and female), as it floated in a dark cabin, emitted 

 clouds of light, which at last lit up the bucket, so that all its 

 contents were visible in the clearest detail ; but the luminous 

 secretion of a female Aristceus was neither so bright nor so 

 lasting. In Pentacheles (female) the light was confined to two 

 points near the openings of the ducts for the eggs. 



The majority of the luminous crustaceans are either pelagic 

 or abyssal, and the habits of those endowed with this property 

 do not appear to differ from those which are not. 



It has been asserted that some of the Bryozoa (Molluscoida), 

 e. g. Scrupocellaria reptans, Membranipora pilosa, and M. mem- 

 branacea, are luminous, but such has not been observed here. 

 They may, however, owe this property to luminous Bacteria. 



The phosphorescent mollusks are represented by bivalves 

 and univalves, and some have been known for a very long time. 

 Thus Pliny mentions Pholas dactylus, which Panceri found to 

 have a luminous border to the mantle, two patches and two long 

 ridges in the branchial siphon. The special epithelium of these 

 parts secretes a phosphorescent substance — soluble in ether and 

 alcohol — which illuminates the excurrent water and the lips of 

 those who eat them. The light is also maintained for a long 

 time during putrefaction, as in the annelid Thelepus. The 

 French chemist, Dubois, separated two substances from the 

 light-producing tissues of Pholas — one crystalline which is soluble 

 * ' Challenger,' vol. xiii. p. 74. 



