INTRODUCTORY. 35 



Moseloy stated that the brilliant illumination created by a large 

 Anthozoon enabled him to read print ; even if it does not 

 generally attain to this degree of brilliancy, a large patch of 

 phophorescent Alcyonarians would give off a considerable 

 amount of light. Round such spots it is believed that the 

 eyed forms congregate. It is not, of course, supposed that the 

 light emanating from the sessile Gorgonias and the Anthozoa 

 has been produced by natural selection, acting on behalf of the 

 creatures to whom the light is considered useful ; that would 

 be an application of the theory too extended for even its most 

 extreme supporters ; the phosphorescence, it is thought, protects 

 these Gorgonians from their enemies ; incidentally, it happens 

 to be useful to the crustaceans and fishes that hover round 

 these well-lighted areas. 



In some cases, however, it is conceivable that the phos- 

 phorescence may have been increased by natural selection as 

 being useful to the animal emitting the light ; certain deep-sea 

 fishes and crustaceans have phosphorescent organs developed 

 on the head or along the sides of the body ; these may even 

 be furnished with lens-like transparent bodies serving to con- 

 centrate the rays of light ; an animal of this kind swims about 

 in the abyssal water, and is guided to its prey by a series of 

 " bull's-eye " lanterns. 



Professor Moseley made, during the voyage of the Chal- 

 lenger, some very important observations upon the nature of 

 the light given out by phosphorescent organisms. Among 

 Alcyonarians, red, yellow and green rays only were detected ; 

 u Hence," remarks Professor Moseley, " were the light in the 

 deep sea derived from this source, in the absence of blue and 

 violet, only red, yellow and green colours could be effective." 

 As a matter of fact, these colours do exist commonly among 

 deep-sea animals particularly shades of red and purple 



