FISHES FROM THE SEA-BOTTOM 427 



turbed, as, for instance, off the north of Scotland. Murray has 

 termed the Hmit of wave-action the mud-lme, and the average 

 depth in the open ocean at which mud commences to be laid 

 down he places at about 100 fathoms. 



Beyond the mud-line the physical conditions become more 

 and more uniform, and for a few hundred fathoms below this 

 limit animal life is exceedingly abundant. This region, accord- 

 ing to Murray, is the "great feeding ground" of the ocean, 

 especially around continental shores ; the organic particles from 

 the continents and from the shallow waters there slowly come to 

 rest on the bottom and supply food to the wealth of crustaceous 

 forms which are captured in such situations (Calantis, Bzickcsta, 

 PasiphcEa, Crangon, Calocaris, Pandahcs, Hippolyte, Pagitmis, 

 Amphipoda, Isopoda, and Mysida). 



The surface layers of the organic deposits which are Decreasing 

 situated in moderate depths towards the central parts of the food"on°pro- 

 ocean basins (Diatom ooze, Globigerina ooze, Pteropod ooze), ceedinginto 

 yield an abundance of food for benthonic animals, but all '^^^p^'^^"- 

 investigations go to show that where the organic oozes pass 

 with increasing depth into Red clay, the quantity of food for 

 bottom-living animals rapidly diminishes, and the number of 

 animals captured on Red clay bottoms likewise diminishes very 

 greatly. The poorest hauls during the whole of the " Challenger " 

 Expedition were those taken in the stretches through the 

 central Pacific from Japan to Valparaiso, and Alexander Agassiz's 

 investigations on board the "Albatross" gave similar results. 

 He calls the central South Pacific a "barren region." 



This short statement will make it obvious, that the condi- 

 tions of life offered to organisms may vary greatly in different 

 depths. Murray's theory on the importance of the deposits to Relation 

 the distribution of animal life is of special value, because it df^^rent kinds 

 opens up to science the possibility of finding certain definable of deposits 

 reasons for the differences observed in the specific composition, Hvfng^on^""^ 

 and in the abundance, of animal life from place to place. them. 



This study has, however, been somewhat neglected as far as 

 the oceans are concerned. Most of the deep-sea expeditions 

 have been so absorbed in faunistic research, that the problems of 

 the economy of the ocean have been very little attended to, 

 and the strong interest taken in theoretical plankton-research 

 peculiar to recent times has drawn attention away from the 

 bottom-life of the ocean and the importance of the deposits as 

 food for the bottom fauna, but Lohmann and C. G. J. Petersen 

 have recently turned attention again to Murray's point of view. 



