THE PELAGIC FAUNA AND FLORA. 185 
Studer gives 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 
1 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. 
