EXISTENCE AND DISTRIBUTION OF MARINE ORGANISMS. 403 



shows that there is a much greater number of species in the Tropics 

 than in the Antarctic, but at the same time a less total amount of 

 organic matter, clue to the smaller absolute number of individuals in 

 the warmer waters. In making this comparison, however, it must be 

 recalled that the metabolism of cold-blooded animals rises with the 

 temperature of the water, and is therefore very much more rapid within 

 the Tropics than at the Antarctic Circle, so that within a given period 

 of time many more organisms may pass through their life history in 

 warm than in cold water, but on account of the high temperature of the 

 water the effete products are more rapidly disposed of than in the cold 

 polar waters, where chemical action is more sluggish. A measure of 

 this rate of change is to be found in the large amount of saline 

 ammonia present in the sea water of the Tropics, while albuminoid 

 ammonia predominates in polar waters. 



When we compare the shallow water animals living on or attached to 

 the bottom within the tropics and toward the polar regions, we find 

 that the distribution follows the same laws as in the case of the pelagic 

 organisms. There are many more species, especially of lime-secreting 

 organisms, in the warm waters of the tropics than in the colder waters 

 toward the poles. For instance, the Challenger's dredgings in the 

 vicinity of Cape York, Australia, in depths less than 12 fathoms, 

 yielded 554 species of metazoa, while many more dredgings at Kerguelen, 

 in depths less than 25 fathoms, yielded only 130 species; indeed the 

 total number of species known from Kerguelen in depths less than 25 

 fathoms amounts only to 242 species. While the number of species of 

 shell-bearing mollusks procured by the Challenger in depths less than 

 12 fathoms at Cape York was 202, only 02 species were taken at Ker- 

 guelen down to 120 fathoms, and the total number known from 

 Kerguelen is only 125 species. The higher Crustacea (macrura, anomura, 

 brachyura) are also more abundant in the tropics, while the reef-build- 

 ing corals are, of course, entirely absent at Kerguelen. On the other 

 hand, the hydroida, holothurioidea, annelida, amphipoda, isopoda, 

 pycnogonida, and tunicata, which secrete little or no carbonate of 

 lime, are more numerous in the cold waters around Kerguelen. 



The recent deep-sea researches have shown that not only is life 

 universally present in great abundance at the surface of the sea, and 

 probably also, though much more sparsely, in all the intermediate 

 depths of the ocean, but also that fishes and all the invertebrate groups 

 are spread all over the floor of the ocean in great numbers. The total 

 number of species taken by the Challenger in depths less than 100 

 fathoms is 4,400; in depths between 100 and 500 fathoms, 2,050; in 

 depths between 500 and 1,000 fathoms, 710; in depths between 1,000 

 and 1,500 fathoms, 600; in depths between 1,500 and 2,000 fathoms, 

 500; in depths between 2,000 and 2,500 fathoms, 340, and in depths 

 over 2,500 fathoms, 235. It is thus seen that the actual number of 

 species procured decreases with increase of depth, and if we take into 



