PELAGIC FAUNA. 123 



according to Moseley, they would seem to prefer a habitation near 

 the mouths of fresh-water streams, being seen to crowd up towards 

 tlie heads of fjords and inlets. In the Hawkesbury inlet, New 

 South Wales, the Scyphomedusse were observed by this natm-alist 

 swimming in shoals where the water was so pure as to be quite 

 drinkable. 



Much uncertainty still exists as to the relation which the free 

 oceanic fauna bears to the fauna of the deep-sea, an uncertainty 

 due to the difficulty of determining the actual depth whence the 

 different organisms caught in the net were obtained. Alexander 

 Agassiz maintains, as the result of experiments made with the 

 Sigsbee net, the most improved appliance thus far invented for 

 the purposes of deep-sea exploration, that "the surface-fauna of 

 the sea is really limited to a comparatively narrow belt in depth 

 [about fifty fathoms], and that there is no intermediate belt, so to 

 speak, of animal life between those animals living on the bottom 

 or close to it, and the surface pelagic fauna."" Beyond a depth 

 of one hundred fathoms nothing was found. On the other hand, 

 the numerous observations made by Mr. Murray on board the 

 "Challenger," with appliances less perfect than those used by Mr. 

 Agassiz, almost conclusively prove that the depth penetration is 

 very much greater than is here indicated, and that possibly a 

 direct continuation exists in the case of certain groups of animals 

 between the pelagic and abyssal faunas. The fact seems to be 

 pretty satisfactorily established, however, that the true zone of 

 free oceanic life, or that which is most numerously inhabited, is a 

 shallow one, and that whatever life extends to great depths is 

 comparatively restricted. 



It would appear that a large proportion, if not the greater num- 

 ber, of the pelagic animals are more or less nocturnal in their habits, 

 shunning the glare of daylight, and appearing on the actual surface 

 only during the hours of evening and night. Such are most of 

 the pelagic fishes, crustaceans, pteropods, heteropods, and fora- 

 minifers, which in their hidden depths for a long time eluded the 

 search of naturalists. The radiolarians, jelly-fishes, and certain 

 crustaceans, on the other hand, seem to prefer the open daylight, 

 appearing at all hours on the surface during calms; and the same 

 is the case with a number of fishes, as the flying-fish and dolphin 

 (Coryphsena). There is thus a perpetual oscillation in this upper 



