196 



THREE CRUISES OF THE " BLAKE. 



Fig. 124. — Hastigerina pelagica. 

 (Clialleiiger.) 



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- 

 ficient amount of sarcode 

 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 feedingf- - orounds for the dwellers of these 

 depths. With the thousands of radiolarians and other pelagic 

 globigerinse 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 



