ANIMAL LIFE IN THE SEA 173 
In the first place it is noticeable that the larger algae 
are unrepresented in the open sea. The weed which 
floats at the surface of the Sargasso Sea is an apparent 
exception, but it is apparent only, for this weed is torn 
off the shores, especially off the Bahamas, and though 
it proliferates vegetatively in the open, and can live 
there for a time, it is not a truly pelagic form. The 
swarms of animals which live among the floating 
masses of weed in the Sargasso Sea show what an 
important addition to the food-supply of the ocean 
the weed is. 
The basal food-supply of the pelagic animals is, 
therefore, the phytoplankton, the minute algae which 
float at the surface. Necessarily these algae, as light- 
demanding organisms, are limited to the surface layers 
of the water, being especially abundant in the upper- 
most 25 fathoms. They occur, though in diminished 
quantity, down to 50 fathoms. Those found in greater 
depths are resting stages or dead forms. The dead 
forms, as we have already suggested, tend to accumu- 
late, at least temporarily, at levels where a sudden 
increase of density occurs. As regards quantity, the 
water of the open ocean seems to be poorer in algae 
than coastal waters, but, as has been already sug- 
gested, currents may carry the shore forms out to the 
ocean, and there is reason to believe that then the fish 
of the shore may follow them. 
The next point to be considered is the distribution 
of pelagic animals. There is a tendency among many 
writers, at least tacitly, to confine the term ‘ pelagic’ to 
those forms which live sufficiently near the surface for 
light to penetrate. There is, however, no real justifica- 
tion for this use. An animal living at a depth of 
2,000 fathoms is as truly pelagic as one living at 
