750 hepoet — 1884. 



in the retinas of deep-sea fish, which may conceivably help towards physiological 

 conclusions as to the functions of the various components. With regard to the all- 

 important question of the nature of the light undoubtedly present in the deep sea, 

 it is hardly possible to accept Professor Verril's recent startling suggestion that sun- 

 light penetrates to the greatest depths with perhaps an intensity at from 2,000 to 

 8,000 fathoms equal to that of some of our partially moonlight nights. Such a con- 

 jecture is entirely at variance with the results of all experiments on the penetration 

 of sea-water by sunlight as yet made by physicists, results which have prevented 

 other naturalists from adopting this solution of the problem. 



The progress of research by experts on the deep-sea fauna confirms the con- 

 clusions early formed that it is impossible to determine any successive zones of 

 depth in the deep-sea regions, characterised by the presence of special groups of 

 animals. Within the deep-sea region the contents of a trawl brought up from the 

 bottom give no evidence which can be relied on as to the depth at which the 

 bottom lies within a range of at least 2,500 fathoms. Some groups of animals appear 

 to be characteristic of water of considerable depth, but representatives of them struggle 

 up into much shallower regions. Thus of the remarkable order of Ilolothurians 

 Elasipoda nearly all the representatives occur at very considerable depths, and 

 their numbers diminish shorewards, but one has been found in only 100 fathoms. 

 Again, the Pourtalesidse range upwards into about 300 fathoms, and the Phormo- 

 somas, which Loven considers as eminently deep-sea forms, range up to a little 

 over 100 fathoms depth, and are nearly represented in shallow water at a depth of 

 only five fathoms by Asthenosoma. As has often been pointed out before, there 

 are numerous genera, and even species, which range even from the shore-region to 

 great depths. 



The fact that zones of depth cannot thus be determined adds seriously to the 

 difficulties encountered in the attempt to determine approximately the depths at 

 which geological deposits have been formed. Dr. Theodore Fuchs, 1 in an elaborate 

 essay on all questions bearing on the subject, has attempted to determine what 

 geological strata should be considered as of deep-sea formation, but, as he defines 

 the deep-sea fauna as commencing at 100 fathoms and extending downwards to all 

 depths, his results may be considered as merely determining whether certain 

 deposits have been found in as great a depth as 100 fathoms or less, a result of 

 little value as indicating the depths of ancient seas or the extent of upheaval or 

 depression of their bottoms. Mr. John Murray has shown that the depths at 

 which modern deep-sea deposits have beeu formed can be approximately ascer- 

 tained by the examination of their microscopical composition and the condition of 

 preservation of the contained pelagic and other shells and spicules. 



The most important question with regard to life in the ocean, at present 

 insufficiently answered, is that as to the conditions with regard to fife of the inter- 

 mediate waters between the surface and the bottom. It is most necessary that 

 further investigations should be made in extension of those carried out by 

 Mr. Alexander Agassiz with similar apparatus — a net, or vessel, which can be let 

 down to a certain depth, whilst completely closed, then opened, lowered for some 

 distance, and again closed before it is drawn to the surface. The greatest 

 uncertainty and difference of opinion exist as to whether the intermediate waters 

 are inhabited at all by animals, and, if they are inhabited, to what extent ; and 

 these intermediate waters constitute by far the greatest part of the ocean. If we 

 estimate roughly the depth of the surface-zone inhabited by an abundant pelagic 

 fauna at 100 fathoms, and that of the zone inhabited by the bottom animals at lOO 

 fathoms also, the average depth of the ocean being about 1,880 fathoms, it results 

 that the intermediate waters, concerning the conditions of life in which we are at 

 present in the utmost uncertainty, really represent more than eight-ninths of the bulk 

 of the entire ocean. Great care should be exercised in drawing conclusions from the 

 depths ascribed to animals in some of the memoirs in the official work on the 

 ' Challenger' expedition. The scientific staff of the expedition merely recorded on 



1 ' Welche Ablagerungen haben wir als Tiefseebildungen zu betrachten ? ' Nevet 

 Jahrbnchfur Mineralogie, Geohgie itnd Palaontologxe, 11. Beilage, Bd. 1882. 





