674 DEPTHS OF THE OCEAN 



phosphorescence " resembles the stars in a clear sky, myriads of 

 minute nearly invisible points emitting a scintillating light, now 

 increasing, now decreasing, in intensity. The " fish-phosphor- 

 escence" appears like great dull bubbles of light which 

 suddenly flare up, as if a dull electric lamp had been turned 

 on and then extinguished, and is produced by large animals, 

 fishes or squids, rushing through the water, sometimes, by the 

 impetus of their movements, causing all the minute phosphor- 

 escent organisms to flare up intensely in response to the 

 irritation produced. That the "dead phosphorescence" is also 

 caused by living organisms has been recognised since time 

 immemorial by fishermen and others who haul ropes or nets 

 through the water at night. Very often small phosphorescent 

 creatures, especially minute crustaceans, are captured and 

 furnish proof that the light is not emitted by the water 

 itself. But scientific men have not always recognised this, 

 for Franklin believed that the phosphorescence of the sea was 

 due to electric sparks caused by friction among the salts of 

 sea-water. According to Steuer, the abbot Dicquemare is 

 supposed to have filtered the sea-water and in this way proved 

 that the water emitted no light. Later on microscopic ex- 

 amination of the minute organisms of the sea has finally proved 

 that the emission of light is inseparable from living substance, 

 and that it is restricted to certain organs built for the sole 

 purpose of this peculiar function of life. 



The power of emitting light is found in most groups of 

 marine animals and plants, beginning with the bacteria. 

 Among plants the peridineans and the remarkable ball-shaped 

 flagellates, Noctiluca viiliaris and Pyi^ocystis noctihica, are 

 noted for their power of emitting light. In animals this 

 power is always attributed to certain structures, which may be 

 said to represent all conceivable forms of glandular develop- 

 ment, from simple epithelial membranes to more or less 

 complicated tubular or lobular glands. These organs secrete 

 a slimy luminous substance. As a rule a layer of black 

 pigment is arranged around the gland, acting as a reflector. 

 Very often the light is projected through a transparent lens- 

 shaped organ. The light - organs thus very often resemble 

 minute eyes, and were previously supposed to perform the 

 function of perceiving instead of emitting light. As we 

 reach the more highly organised groups in the animal kingdom 

 the structure of light- organs exhibits an increasing complexity. 

 In minute crustaceans (see Fig. 492) we very often find only a 



