PHOTOGENIC MARINE ANIMALS. 5 



the abysses of the ocean, it might be supposed that traces of a 

 general resemblance in habits, structure, or physiology would be 

 found, and which would at least indicate the bearings of a pro- 

 vision so important. Thus, for instance, a similar state of 

 matters might be expected in the dark caverns of Illyria and 

 Dalmatia, or in those of the mammoth caves of Kentucky. 



On surveying the marine animals possessed of this property 

 of phosphorescence, however, they are found to live under circum- 

 stances so diverse that it is truly difficult, not to say hazardous, 

 to promulgate any theory of the foregoing kind in connection 

 with this manifestation. 



The lowest forms (Protozoa) which show emissions of light 

 are certain Infusoria, e.g. Ceratium (considered by some to be an 

 alga) and Porocentrum. Our waters teem with multitudes of 

 these, the tow-net in July and August being coated with them, 

 Peridinium, and others ; and if, on removing it from the water 

 at night, it is suddenly jerked, the whole interior is lit up with a 

 luminous lining, which glows brightly for a few seconds and 

 then fades. The same forms cause the crest of each wave as it 

 curls from the sides of the boat to sparkle vividly. Other phos- 

 phorescent Protozoa are the Piadiolarians — Collozoum, Spheero- 

 zoum, and Thalassicolla — which Giglioli found to shine with an 

 intermittent greenish light in the Pacific. No member of the 

 group, however, is so well known for its photogenic properties as 

 Noctiluca, a minute, transparent, gelatinous sphere, which is 

 very widely distributed throughout the warmer seas. Its minute 

 size and vast abundance probably gave rise to the old notion that 

 the luminosity of the sea was due to the water itself, and not to 

 any visible organism. Thus an ecclesiastic named Tachard 

 (1686) considered that the water absorbed the light of the sun 

 by day and emitted it at night ; whilst Eobert Boyle attributed 

 the phosphorescence of the waves to friction with the air.* To 

 M. Pdgaut, an acute French surgeon, belongs the credit of being 

 one of the earliest observers to prove that the phosphorescence 

 of the sea off the French coast and off the Antilles was due to 

 this organism, which he called a little spherical polyp. It occurs 

 in vast swarms in most of the great oceans, and even off the 

 southern and western shores of Britain, and is the cause of that 



* Phipson, ' Phosphorescence,' p. 174, 1862. 



