570 



NATURE 



[April 1$, 1880 



What is wanted to determine the problem 15 a net 

 which can be let down to any required depth, securely 

 closed, then be opened and towed for some time, then 

 closed again and brought to the surface. Its contents 

 would then be certainly derived from the depth at which 

 it was towed. I devised, some months ago, a net which 

 will, I believe, answer these requirements. Its mouth, 

 which is fastened on a hinged frame, is kept shut by 

 means of springs, but can be opened by the action of a 

 pair of electromagnets excited by a battery on board 



Fjg. ii.— Arenaceous Rhizofoda. a, Astrort.iza catena/a, 2,760 fathoms; 

 i, Sorosphara. confusa, 900 to 2,900 fathoms; c, Hyfcrammina vagans 

 attached to a piece of shell, 2.000 fathoms. (After H. B. Brady, F.K.S., 

 Quart. Jomn, Micro. Sci., vol. xix., new series). 



ship. A rope is used to tow the net, which contains an 

 insulated wire. Whilst the net is being towed, the 

 magnets are maintained in action and keep its mouth 

 open. As soon as the net is to be drawn to the surface 

 the current is stopped, and the net closes. Mr. Agassiz 

 intends to use this net or some better contrivance during 

 this summer on the American coast, and we may await 

 the results with great interest. 1 



It has long been known that pelagic animals change 

 their level constantly, appearing sometimes in swarms at 

 the very surface of the sea, and again disappearing. Some 

 come up in calm weather, others only at night, but it is 

 quite uncertain to what depths they descend. Probably 

 the different pelagic animals vary very much in this 

 respect, and they may each have their definite zones of 

 range. It would be most interesting to learn the exact 

 habits of such animals as Pteropods in this matter. The 

 question could easily be determined by the use of such a 

 net as I have described for a short period at any one 

 locality, and most valuable results might be obtained by 

 any one who cared to take the matter up in the neigh- 

 bourhood of our own coasts. 



Very possibly the pelagic animals do not range to any- 

 great depth, 100 or 150 fathoms, or less. Prof. Weissman 

 concludes from his researches at Lake Constance that 

 the surface animals there sink to a depth of about 50 feet 

 in the day-time in order to escape the sunlight, and 

 rise slowly in the evening, following the rising limit of 

 darkness in the water. 



It is quite possible that a vast stretch of water between 

 the surface and the bottom is nearly or absolutely without 

 life. 



There are a large number of animals, some of the most 

 curious forms, which most probably do not live at the 

 bottom of the sea, but which constantly appeared in our 

 trawl-net when used in great depths. Amongst these are 

 a large number of fish of great rarity. They may have 

 ■come from 20 fathoms or from 2,000. We cannot tell. 

 Possibly they live at 60 or 100 fathoms, and rarely reach 

 the surface ; hence their scarcity. Some certainly pelagic 

 animals, which are very scarce, probably live at a consi- 

 derable depth from the surface. 



Here (Fig. 12) is a very scarce animal indeed, a pelagic 

 Nemertine worm. The Nemertines mostly live on the sea- 

 bottom, and are long and worm-like. This is one which 

 has become so modified to live a pelagic existence as to 

 resemble them in appearance very little. Its body has 



1 Since this lecture was sent to the printers I have heard from Mr. Agassiz 

 that Capt. Sigsbee has invented a net which he expects will do all that is 

 ■wanted with complete efficiency. 



become transparent like glass, that the animal may become 

 almost invisible to its enemies, whilst the branching intes- 

 tine, the only part which could not be rendered translucent, 

 has become brown-coloured, as in several other pelagic 

 animals, to imitate floating sea-weed. The proboscis pro- 

 jected from the head shows the animal at once to be a 

 Nemertine. I have called it Pelagonemertes. Onespeci- 



Fig. 12.'— Pelagonemertes Rollestoni. On the left the proboscis sheath with 

 the proboscis coiled up inside. 



men of this animal was found in the trawl after it had been 

 down to i,Soo fathoms, to the south of Australia. An- 

 other was got off Japan when the net had been down to 

 755 fathoms. The animal was only found on these two 

 occasions at these widely distant spots. Fifty years ago 

 Lesson, on the voyage of the Cequille, found in abund- 

 ance, on the sea-surface between the Moluccas and New 



About one-sixth of the 



Guinea, a closely allied animal, the nature of which he 

 failed to understand. He must have fallen in with the 

 animals just when they were at the surface. No doubt 

 they are abundant at some depth or other all over the 



It seems probable that some animals which live near 



■ From "Notes by a Naturalist," p. 573- 



