RELATIONS TO OTHER SCIENCES 691 



cumulated towards the tropics through the action of lime-secreting 

 organisms which obtain the lime from the sulphate of lime in sea- 

 water. 



The great abundance of pelagic larvae of benthonic organisms 

 in warm tropical surface waters, their periodicity in the intermedi- 

 ate zones with a wide range of temperature, and their almost total 

 absence in polar waters and in the deep sea, are facts in distribution 

 of great interest to the biologist and evolutionist, and may be ac- 

 counted for by the varied temperature conditions in the several 

 areas. 



The temperature conditions in the deep sea and on the floor of the 

 ocean form a striking contrast to those prevailing in the surface 

 waters. The lines of equal temperature, instead of running parallel 

 to the equator, as at the surface, run on the whole north and south, 

 following the general trend of the continents. The water which 

 rests immediately on the ocean's floor in great depths has nearly 

 everywhere a temperature under 40 F., and a very large part of it 

 is below the freezing-point. Only a small band running north and 

 south in shallow water along the continental shores has a tempera- 

 ture over 40 F. It follows, then, that much more than one half 

 of the solid crust of our globe is kept at a low temperature at all 

 times. The abysmal regions have not only a low temperature, but 

 eternal darkness reigns there so far as the sun's rays are concerned; 

 any motion which takes place in the water must be of extreme slow- 

 ness. Transport and erosion do not take place in this deep region, 

 which is an area of deposition. The materials composing the de- 

 posits, being saturated with sea-water during immense periods of 

 time, become highly altered, and secondary products are formed 

 in and on the surface of the deposits, such as manganese-iron 

 nodules, palagonite, and zeolitic crystals. 



The animals which have been able to accommodate themselves 

 to life in the abysmal regions derive their food primarily from the 

 dead organisms and excreta which have fallen from the surface 

 waters: they are, indeed, mud-eaters. There is much reason to be- 

 lieve that the whole of the marine deposits are sooner or later 

 eaten by organisms; it is, indeed, probable that all stratified rocks, 

 whether marine or lacustrine, have in like manner passed through 

 the intestines of animals. In many instances the excreta of the 

 benthonic animals are converted into glauconitic and phosphatic 

 grains. Phosphorescent light plays a large part in the economy 

 of marine organisms, and it is a remarkable fact that this phenomenon 

 of phosphorescence has never been observed in any fresh-water 

 organisms. Some deep-sea animals are blind, some have very large 

 eyes, some have highly developed tentacular organs. Some have 

 complicated organs for the emission of light, some are many times 



