406 RAMBLES OF A NATURALIST. [Ch. XXIII. 



The animals which I have observed to possess luminous 

 properties are not numerous. Many of the more minute 

 animals taken in the towing-net appear to exliibit them, 

 more particularly the small Crustacea (Entomostraca), and 

 smaJl Medusae (Medusidse). I have no reason to believe 

 that the larger Medusae (Lucernaridse) as Aurelia, Pelagia, 

 Ehizostoma, &c., exhibit any luminous powers, having kept 

 specimens which have invariably failed to do so. Nor 

 have I any experience of the Physophoridae becoming lu- 

 minous. I have never seen a luminous Porpita or Velella, 

 and although on one occasion when magnificent specimens 

 of Portuguese men-of-war had been floating by all day, 

 my attention was directed to shining spots at night, under 

 the supposition that they were lyminous Physahae, I merely 

 replied by pointing to a bucket containing one of these 

 animals, but which was perfectly dark. I have seen a 

 large prawn give out Ught after death, and a fresh squid 

 was illuminated at night with an irregular glow of whitish 

 light, which remained unaltered as I passed my finger 

 over the surface. Nor db I believe many of the stories 

 of luminous fish, inasmuch as a fish rapidly swimming in 

 a fiuid abounding in minute luminous points, as the sea 

 sometimes does, would present an efiect which an unin- 

 formed or inaccurate observer would readily mistake as 

 proceeding from the fish, itself, instead of from luminous 

 points which it disturbed in its passage. 



Few luminous marine animals have received greater at- 

 tention than the Noctilucae, and from them we may perhaps 

 gather some indications of the seat and nature of this won- 

 derful appearanee. M. De Quatrefages concludes, as the re- 

 sult of his experiments with these Protozoa, that they retain 

 their luminosity so long as they continue to possess organic 



