LIFE IN THE SEA 477 



by taking in each other's washing. Ultimately, the 

 source of food is the plant life of the plankton, or the 

 organic materials washed from the littoral zone or the 

 rivers. There is a continual rain of minute organic 

 particles from above, slowly sinking to the bottom. 

 Along with this falls the multitude of shells or tests of 

 radiolaria, foraminifer'a, and diatoms. Thus the open 

 ocean comes to have its floor composed of such material 

 as the radiolarian ooze, composed of millions of minute 

 tests of these Protozoa. In the deeper seas, life at the 

 bottom exists under peculiar circumstances. It is very 

 cold, and entirely dark, except for the phosphorescence 

 of the animals themselves. The pressure of the water 

 is enormous, but the animals do not feel it, since 

 their internal fluids have a density to correspond. On 

 being quickly drawn to the surface, however, they 

 tend to explode as it were, to fall to pieces. It is not 

 always easy to determine whether fishes have been 

 caught on the bottom, or were captured as the net was 

 being drawn up. Thus, for example, the fish Alepo- 

 cephalus has been taken by many deep-sea expeditions, 

 and was regarded as a typical example of the benthos 

 of the depths ; but on one occasion a tow net was 

 dragged about a thousand meters above the bottom, 

 and an Alepocephalus was captured. 



7. The fauna of the sea affords endless opportunities Ourimper- 

 to the naturalist who wishes to solve scientific and e d C geofsea 

 economic problems. Even the easily accessible littoral Ufe 

 fauna of our own shores is still imperfectly known ; 

 thus many new mollusks have been described from 

 the coasts of California in recent years. The life 

 histories of innumerable forms remain to be investi- 

 gated. When we come to the deep sea, the extent of 

 the problem is almost appalling. So far, we have 



