498 LIFE ON THE OCEAN SURFACE. 



delicate tubular calcareous spines, such as Globigeriim and its 

 allies, which float everywhere on the surface, and the dead 

 shells of which form the vast calcareous deposits on the deep- 

 sea bottom known as Glolngefiiia mud. 



At night, the pelagic animals render themselves conspicuous 

 by their phosphorescence. The kind of light emitted, and the 

 manner of its appearance, varies according to the nature of the 

 animal causing it. Sometimes the sea far and wide, as far as 

 the eye can see, is lighted up with sheets of a curious weird- 

 looking light, and wherever the water breaks a little on the 

 surface before the breeze, the white foam is brilliantly illu- 

 minated. This particular kind of illumination is due to 

 Noctiluca. One night, when we were between the Cape Verde 

 Islands and St. Paul's Rocks, the sea was thus illuminated by 

 myriads of Nodilitca, and the lower sails of the ship were seen 

 to be distinctly lighted up by the light given off from the 

 broken water thrown up by the hull of the vessel. 



At other times, the water where disturbed is seen to be full 

 of small luminous scintillating specks. This is the commonest 

 form of phosphorescence, and is due to various small animals, 

 principally small Crustacea, which give out their light thus by 

 flashes. Some Crustacea certainly derive their phosphorescence 

 from containing in their stomachs phosphorescent food, and 

 their excrement is phosphorescent, as was first pointed out to 

 me by my friend. Captain Tupman, R.M.A. When large fish, 

 or porpoises or penguins, dash through water full of luminous 

 Crustaceans or Noctiluca^ their bodies are brilliantly lit up, and 

 their tracks marked by trails of light. 



The most beautiful kind of phosphorescence is however that 

 of the Ascidian colony Pyrosoma. This, when stimulated by a 

 touch, or shake, or swirl of the water, gives out a bright globe 

 of bluish light, which as the animal drifts past several feet 

 beneath the surface lasts for several seconds and then suddenly 

 goes out. 



A giant Pyrosoma was caught by us in the deep-sea trawl. 

 It was like a great sac, with walls of jelly about an inch in 

 thickness. It was four feet in length, and ten inches in dia- 

 meter. When a Pyrosoma is stimulated by having its surface 

 touched, the phosphorescent light breaks out at first at the spot 

 stimulated, and then spreads over the surface of the colony as 

 the stimulus is transmitted to the surrounding animals. I 

 wrote my name with my finger on the surface of the giant 

 Pyrosoma, as it lay on deck in a tub at night, and the name 

 came out in a few seconds in letters of fire. 



Pelagic animals range through a considerable depth of 

 water, near the surface of the sea, ascending to the surface at 



