574 A NATURALIST ON THE " CHALLENGER." 



Most important to the student of deep-sea phenomena, are 

 the Foraminifera with calcareous shells, covered with long 

 delicate tubular calcareous spines, such as Globigcrina 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 of Globigerina 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-look- 

 ing light, and wherever the water breaks a little on the surface 

 before the breeze, the white foam is brilliantly illuminated. 

 This particular kind of illumination is due to Noctiluca. One 

 night, when we were between the Cape Verde Islands and 

 St. Paul's Ptocks, the sea was thus illuminated by myriads of 

 Noctiluca and the lower sails of the ship were seen to be dis- 

 tinctly 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 first pointed out to me 

 by my friend, Captain Tupman, E.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 track marked as a trail 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 

 blueish light, which lasts for several seconds, as the animal drifts 

 past several feet beneath the surface and then suddenly goes out. 



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

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

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



