Til?: I'p]LAGIC f'ACXA AND FLORA. 185 



Stiider ^ives a list of the depths from which Rhizophysa came 

 up attached to the sounding-line ; but it is by no means certain 

 that these siphonophores belonged in the depths indicated by 

 the wire. They may have become caught on the wire while it 

 was reeling in at only a short distance from the surface.^ The 

 fact that Studer never succeeded in bringing up any of these 

 species in the tow-net, even when it was lowered to a consider- 

 able depth, is equally inconclusive, since, at any rate in the Ca- 

 ribbean Sea, their isolated parts and fragments are not infre- 

 quently found floating on the surface. It is probable that they 

 usually live at a constant depth below the surface, and some of 

 them may, like Polyclonia, prefer to dwell near the bottom. 

 But until we possess a net so constructed as to give some sure 

 indication of the intermediate depths at which the animals living 

 at various distances between the surface and bottom have been 

 gathered in, it seems hazardous to define the bathymetrical range 

 of a large number of pelagic animals, such as the acalephs, 

 siphonophores, heteropods, pteropods, numerous foraminifera, 

 radiolaria, and the like, the habits of which are scarcely 

 known. 



In the case of fishes, dredged in deep water at a moderate 

 distance from the land, we ought not to take it for granted that 

 they invariaby live at the depth to which the trawl may have 

 been lowered. The young of many of the deep-water fishes are 

 undoubtedly pelagic, often till a late period of growth, and this 

 would account for the discovery of many of the deep-water 

 fishes, especially in the proximity of oceanic islands or around 

 coasts situated near deep water. 



Of the acalephs, the greater number of the ctenophores, many 

 of the discophores and a few sertularians, are pelagic ; the ma- 

 jority of the hydroids and some of the discophores are pelagic 

 only during a period of their existence, and remain the rest of 

 the time attached to the bottom ; as fixed hydroids, they extend 

 into deep water. A number of families of discophores are 



* In one case, when we were dredging wire .' On another occasion, the same 



in one thousand fathoms, numerous frag- species came up after we had drawn in 



ments of a Rhizophysa came up after we three hundred fathoms, while dredging in 



had drawn in one hundred fathoms of five hundred fathoms. 



