1904-1905.] 333 



about two miles in depth to the extreme limit of five and a 

 half miles. Our fishing area is a mere shelf on the margin of 

 the Atlantic basin, and the transition from the shallow waters 

 near our coasts to the great depths is very sudden. Till re- 

 cently next to nothing was known of the depths of the sea, 

 but the Challenger expedition, under the late Sir Wyville 

 Thompson, added greatly to our knowledge, and numerous 

 later investigations have further extended it. There were 

 many difficulties encountered by the first explorers of the 

 abysses, but these have gradually been overcome, and now it 

 is possible to use even such large apparatus as a fifty-foot 

 otter-trawl at depths of more than a mile. Special apparatus 

 has been devised for obtaining samples of the bottom and 

 samples of water, as well as for the capture of specimens of 

 the organisms that live at various depths. For a time there 

 was a controversy as to whether the animals brought up in 

 the bottom nets were not largely caught during the hauling 

 up of the nets; but doubts on this subject have been set at 

 rest by " closing nets " that are arranged to work at given 

 depths, and are then closed. Investigations show that the 

 bottom waters of our oceans are cold, varying little in tem- 

 perature from year to year, and that they are dark, and that 

 the pressure exercised by the superincumbent waters is enor- 

 mous. This last fact is of importance, as it implies that 

 migration is greatly restricted by th..- pressure, and it is of 

 special interest to the zoologist, as it explains why he so rarely 

 gets a perfect fish from the bottom of the ocean ; usually the 

 parts are greatly strained as the result of the release of pres- 

 sure. It may be asked, How do animals live in such environ- 

 ment ? There are no plants living there on which the ani- 

 mals may feed, so that all life is dependent on what may fall 

 from above. But even so, it is difficult at first to realise how 

 food is found. Some fishes adopt what has been called a 

 " masterly policy of inactivity,' and wait for food to enter 

 their mouths. Others seem to depend on luminous organs to 

 enable them to find their prey, and certain of these forms are 

 of special interest, because they are related to common shore 



