tion of fish. 



FISHES FROM THE SEA-BOTTOM 431 



tained in the deposits, which fertilises the surface layers of the importance 

 Blue mud as well as of the Globigerina ooze. maufr^?n^he 



Petersen has shown that only the uppermost layer of the deposits. 

 mud contains organic detritus, but the quantity of organic 

 substance deposited is not always the most important factor. 

 Where the water is in motion at the bottom, a fine cloud of influence of 

 organic matter is swept along, and in such localities the mud- ^^H'^^^l ^^ 

 eaters thrive in great quantities. The fishermen have for a the distribu 

 long time profited by this fact, for they do not seek those places ' ^""^ 

 (as in pits and channels on the bottom) where mud is laid 

 down, but choose rather the spots where the bottom is covered 

 with coarser particles, and where the finest mud cannot settle. 

 In these places the fish find most food, and the fishermen most 

 fish. 



Perhaps conditions like these prevail on the eastern Atlantic 

 slope, as, according to the current-measurements of the 

 " Michael Sars," considerable currents extend down to great 

 depths. All such conditions call for further examination, 

 especially in the open ocean, and it may be affirmed that studies 

 of this kind will be essential for an understanding of the 

 quantity of life along the bottom. 



Returning to the question of the geographical distribution of 

 different species of fish, we may now examine some of the 

 conditions which influence that distribution, according to the 

 present state of our knowledge. 



We have seen that the species Macrttrus arniatus is known 

 from the abyssal plain in the Pacific as well as in the Antarctic 

 and Atlantic Oceans. The chart (Fig. 308) indicates the 

 localities of capture and also the temperature, and shows at a 

 glance that, notwithstanding the immense geographical range of 

 this species, it is taken only where the range of temperature 

 is very small (1° to 3^ C). The species is not local ; it is not 

 limited by distance, but by certain physical conditions, which in 

 this case prevail over an immense geographical area. 



Temperatures in abyssal depths are, as we have seen in 

 Chapter V., on the whole very uniform. It is therefore interest- 

 ing to note that it is especially the abyssal forms that are known 

 from wide areas ; thus, for instance, Macrurtis filicatida, known 

 from the Pacific and Antarctic, has a bathymetrical range from 

 2515 to 4843 metres. Macrnrns parallelus, known from New 

 Zealand, Japan, Ceylon, South-west Africa, ranges down to 1300 

 metres. Halosauropsis 7nacrochir, known from the Southern 



Distribution 

 of different 

 species of fish. 



