IIAT^EAH" SOCIETY OF LOKDO>'. 43 



open question of the existence of a mid-water fauna by exact 

 experiments with the intermediate tow-net invented by Tanner*, 

 by which the American Naturalists claim to tow at any given 

 depth, and to exclude entries Irom all other zones of depth. This 

 net was used on the present cruise at 14 stations, at several more 

 than once in various depths. 



Murray and Studer t contend that the bathymetrical zones 

 intermediate between the zone of the pelagic and that of the 

 abyssal bottom fauna are inhabited b}' a distinct fauna. They 

 are supported in this by Chun X, ^ho used a towing apparatus in 

 the Mediterranean to a depth of 65C fathoms, and still deeper on 

 a voyage to the Canary Islands, coming to the conclusion that 

 the pelagic fauna existed all the way down to the bottom. The 

 results obtained by the Prince of Monaco §, with another special 

 apparatus invented b_y himself, were of a similar character ||. 



Agassiz maintains that there is no such mid-water fauna. He 

 thinks that his experiments in truly oceanic areas, with the Sigs- 

 bee gravitating trap from the ' Blake ' as well as with the Tanner 

 tow-net from the ' Albatross,' are conclusive, as he never suc- 

 ceeded in capturing animals in the intermediate zones. He 

 admits that the surface-fauna may temporarily descend to as 

 great a depth as 200 fathoms in order to escape from some 

 surface molestation, and that bottom animals may rise to some 

 60 fathoms from the bottom, but believes that the intermediate 

 zones are azoic. 



He accounts for the different results obtained by the other 

 observers partly by the defective construction of the instruments 

 used, which allowed surface animals to enter whilst the instrument 

 passed through the surface zone, partly by the conditions which 

 obtain in an open oceanic area, and which differ from those in an 

 enclosed sea like the Mediterranean or Californian Grulf, or in an 

 area close to land. He appeals to the fact that the high tem- 

 peratures of the deep water in enclosed seas, as well as the dis- 

 turbing tidal and subvertical currents in the proximity of land, 

 must bring about a bathymetrical distribution of animal life 

 different from that in mid-ocean. 



Agassiz's criticisms of the methods applied by others are very 

 just ; but, on the other hand, John Murray's numerous experi- 

 ments made on board the ' Challenger ' with an open tow-net at 

 different depths in the same locality are not less convincing ; he 

 having fouud invariably a ditierent set of animals with increasing 

 depths, the deeper haul enclosing the animals of the zone or zones 



* This is so large that it can only be worked from large vessels by steam- 

 power. Mr. Townsend has i*ecently constructed a smaller one which can be 

 worked from a boat (Eep. U.S. Fish Commiss. 1894, p. 279). 



t Zeitschr. wiss. Zool. xxxi. 1878, p. 1. 



J Biblioth. Zoolog., I. Die pelaj^ische Thierwelt in grosseren Tiefen, 1887 ; 

 and SB. Akad. Wiss. Berlin, xxx. 1889, p. 519. 



§ Compt. Eend. du CoDgres internal. Zuol. Paris, 1889, p. 133. 



II I pass over tlie observations made by the Italian vessel ' Vettor Pisani ' as 

 thoroughly inconclusive. 



