LIFE ON THE OCEAN SURFACE. 575 



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 my 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 times, 

 especially at night when safe from enemies, and again descend- 

 ing. It is quite uncertain to what depth they extend their 

 rano-e, and whether there is a zone of water intermediate between 

 that near the bottom and that near the surface, which is devoid 

 or nearly devoid of life, as is believed by Sir Wyville Thomson 

 to be probably the case. 



The trawl net used on board the "Challenger" swept, in 

 going down to the deep-sea bottom and in coming up, the entire 

 depth of the sea, and animals were constantly being found in the 

 net, about which it was quite uncertain as to what depth they 

 came from. Amongst these were, for example, some Medusae, 

 which have been found by Prof. Haeckel to be of peculiar 

 structure, and which may possibly be deep-sea forms ; they 

 may, however, also have come from a few fathoms depth only. 



A net of some kind is required to settle this question which 

 shall be capable of being sent down completely closed to any 

 required depth, then opened and towed for some time, and then 

 again closed before it is raised. It is by no means an easy 

 matter to devise such a net which will be practically available. 

 There are numbers of animals, fish, Medusae, and Actinias for 

 example, which are found in the deep-sea trawl, and about which 

 it is a matter of speculation only as to the depth from which 

 they came. 



Mr. Murray hit upon the expedient of using the ordinary 

 towing net at considerable depths* and with great success, since 



* A. Baur was, I believe, the first to use the towing-net at considerable 

 depths. " Beitrage zur Naturgeschichte der Synapta digitata." Verhandl. 

 der K.L.C.D. Akad. 1864. Mr. Murray, however, invented the method 

 independently. 



