SUMMARY 491 



worms, and certain species of small crab-like animals 

 liberate from the surface of their bodies slime that glows 

 like a torch. In many fishes and several squids eye-like 

 phosphorescent organs are imbedded in the skin in vari- 

 ous parts of the body and the phosphorescent or glowing 

 material is backed up by a reflector and the light is 

 made to shine through a lens after the fashion of a bull's 

 eye lantern. In certain localities it is known that 

 the organic matter on the ocean floor contains great 

 numbers of bacteria, or small unicellular plants, that 

 are also luminous. Hence it is believed by many students 

 of the subject that the ocean depths, though devoid of 

 sunlight, may nevertheless be feebly illuminated by 

 phosphorescent light. This would perhaps account for 

 the great owl-like eyes of several deep-sea animals, al- 

 though it is to be noted that many species are totally 

 blind. 



The use of these phosphorescent organs is somewhat 

 problematical. In some species they are almost certainly 

 used to attract organisms that serve as food. In other 

 cases they may serve to drive off enemies or be used as 

 signals to attract the opposite sex. 



Summary. — Plant life in the ocean comprises a 

 scanty fringe of algae attached in the shallows along 

 shore, and widely distributed and exceedingly abundant 

 unicellular species floating near the surface. Vast num- 

 bers of individuals of this last class are continually set- 

 tling to the bottom, and at all depths are fed upon by 

 various species of animals. This floating population, 

 or plankton, thus extends from the surface to the bot- 

 tom, though the larger proportion is confined to waters 

 less than a mile in depth. On the ocean floor other 

 animals crawl over or through the mud or are anchored 

 in it. 



Deep-sea exploration, as a science, is less than fifty 

 years old and much regarding the distribution of marine 

 organisms remains to be learned before we can deter- 



