750 



KBFORT — 1884.. 



^ii 



in the retinas of deep-sea fish, which may conceivably help to-\vards physiologieal 

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

 important question of the nature of the light undoubtedly present in the dwp sea 

 it is liardly possible to accept Professor Verril's recent startling suggestion tlmi sm-' 

 light peiKjtrates to the greatest depths with jierhaps an intensity at from ii,(JOO tj 

 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 peuetratiun 

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

 other naturalists from adopting this solution of the probltuu. 



The progress of research by e.xperts on the deep-sea fauna confirms the con- 

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

 di>pth in the deep-sea regions, characterised by the presence of special groups ^ii 

 animals. Within the dee])-sea region the contents of a trawl brought up from tb'; 

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

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

 tobecharacieristicof water of considerable ilepth, but representativesof them striitrijle 

 np into much shallower regions. Thus of the remarkable order of liolothurians 

 Elasipoda nearly all tlie representatives occur at very considerable dt iths, nnd 

 their numbers diminish sliorewards, but one has been found in only lUU ikthnms, 

 Again, the Pourtalesid.ie range upwards into about .'300 fathoms, and the Phorniii- 

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

 over 100 fathoms depth, and are nearly represented in shallrnv water at a deptli (if 

 only five fathoms by ^■Mhcnosonia. As has often been jiointed out before, there 

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

 great depths. 



The fact that zones of depth cann<it thus be determined adds seriously to tV 

 difficulties encountered in the attemjit to determiiie approximately the depths at 

 which geological deposits have been formed. ])r, Theodore Fuchs,' in an elahowte 

 essay on all questions bearing on the subject, lias attempted to determine wliut 

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

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

 depths, his results may be considered as merely determining whether certai:: 

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

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

 depression of their bottoms. Mr. John 3Iurray has shown that the depths a* 

 which modern deep-sea deposits have been 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 pitSirMt 

 insufiiciently answered, is that as to the conditions with regard to life 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 he let 

 down to a certflin depth, whilst completely closed, then opened, lowered for sonic 

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

 uncertainty and difierence of opinion exist as to whether the intermediate water< 

 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 pehifrir 

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

 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 buli 

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

 depths ascribed to animals in some of tlie memoirs in the ofiicial work on tbe 

 ' Challenger ' expedition. The scientific stall' of the expedition merely recorded ou 



' < Wclchc Ablagorungen liaben wir als Tiofseebildungen zu betrachten ? ' ..AfW 

 Jali/rbvchfur Mincralogic, Gcologie vnd Paliiontolorjic, 11. Hcilage, Bd, 1882. 



