196 THREE CRUISES OF THE “ BLAKE.” 
tigerina (Fig. 124), are pelagic, there is a host of other are- 
naceous forms, perhaps 
the majority of the fora- 
minifera, which certainly 
live at the bottom. Both 
the pelagic and bottom spe- 
cies form a most impor- 
tant factor in the food sup- 
ply of the abyssal fauna. 
The modern greensand 
found along the edge of 
the Gulf Stream proves 
that multitudes of dead 
tests constantly drop 
from the surface, and 
when they reach bottom, 
< they still contain a suf- 
Fig. 124. — Hastigerina pelagica, 8. ficient amount of sarcode 
simi i to make an excellent meal 
for some abyssal echinoderms. The species that live on the 
bottom, and in some localities must thickly cover its surface, 
afford excellent feeding-grounds for the dwellers of these 
depths. With the thousands of radiolarians and other pelagic 
globigerine occur minute protozoa, their capacity for floating 
being increased by the huge spines or extensile pseudopodia 
which they stretch out in every direction. The depth at which 
so-called pelagic foraminifera have been found depends upon 
the fact that, during rough weather or under unsuitable cir- 
cumstances, they sink to a considerable depth, and, while they 
would strictly come within the definition of pelagic animals, 
they may thus frequently be found living apparently on the 
bottom. 
One of the most common of the pelagic protozoa is a spe- 
cies of the genus Noctiluca. (Fig. 125.) On favorable nights 
it forms a thin sheet of phosphorescence, as it were, spread 
over the sea. The tow-net, when dragged during the night, 
reveals the phosphorescent color characteristic of different 
groups, and one who is accustomed to such nocturnal pelagic 
