80 THE ATLANTIC. [chap. ii. 



phosphorescence seemed to be chiefly due to a large Pyrosoma, 

 of which we took many specimens with the tow-net, and which 

 glowed in the water with a white light like that from molten 

 iron. 



Pyrosoma is a free - swimming colony of simple ascidians 

 having the form of a lengthened cylinder 100 mm. to 120 cc. 

 in length, with a cavity within from 20 to 80 or 100 mm. in 

 diameter, open at one end, and closed and coming to a point at 

 the other; the separate individuals, often to the number of 

 many thousands, each included in its proper transparent test 

 of a consistency between jelly and cartilage, make up the wall 

 packed vertically side by side, with all their inhalent openings 

 turned outward, and the exhalent openings turned inward into 

 the cavity of the cylinder. A perpetual current is driven 

 through each animal by the action of the cilia bringing in 

 freshly aerated water to a beautifully fenestrated gill -cavity, 

 and supplying nourishment to a simple stomach and alimentary 

 tract. The consequence of this arrangement is that the water, 

 constantly flowing inward through the myriad mouths on the 

 outer wall, and finding egress only by the open end of the cyl- 

 inder, the colony is moved steadily througli the water, the 

 closed end first. Each animal is j)rovided with a fairly devel- 

 oped nervous system, and the whole can act in concert so as to 

 direct the genend movements of the colony. 



Besides Pyrosoma, there were large numbers of copepod crus- 

 taceans, each of which, on being shaken in the curls of the wave, 

 emitted a spark of light of great intensity, and the breaking 

 water seemed filled with these glittering points. The tow-net 

 brought up during the day, but more particularly toward even- 

 ing, an enormous number of j)elagic animals, most of them more 

 or less phosphorescent. Among them, perhaps predominating 

 in numbers, were decapod crustaceans in the " zoea " and " me- 

 galopa " stages of development ; a great Phyllosoma, 12 cc. 

 from tip to tip of the limbs ; several species of Leucifer / a 



