16 



THE EXPLORATION OF THE SEA 



[part I 



by Bidder in the North Sea^. Then we have several most ingenious 

 pieces of apparatus devised in order to estimate the rate of flow of 

 slowly moving surface and bottom currents. The elucidation of 

 the mode of action of these apparatus I leave to the reader^. 



We have considered these methods of physical observation 

 since they are fundamental to any attempt to discuss what we 

 may term the metabolism of the sea. We have now to consider 

 the methods by means of which the biology of the sea has been 

 investigated. I except the laboratory methods of study of the 

 physiology and development of marine organisms and deal here 

 only with the apparatus of collection. Marine creatures have the 

 most diverse habits of life : some live in the mud at the bottom of 

 the sea, others on the surface of the deposits there, others at the 

 surface of the water, and others again at all intermediate levels. 

 They are of great diversity of size, from that of a micrococcus 

 (1 — 5 thousandths of a millimetre) to that of a large fish or marine 

 mammal such as a whale. Therefore our collecting apparatus has 

 to be adapted to the mode of life and size of the creatures which 

 it is desired to obtain. Ordinary fishing implements may be 

 classified into bottom fishing instruments such as the trawl, 

 dredge, line or set-net ; and into pelagic implements like the 

 seine-net, drift-net or tow-net. The former fish at the sea bottom 

 and catch the organisms which live there, while the latter work 

 at the surface or at any intermediate level and catch the animals 

 or plants which live a pelagic life swimming or drifting about in 

 the body of the sea. 



The dredge and trawl. The dredge. Fig. 6, is the older 

 instrument. It consists of a rectangular iron frame which is from 



/^ 



Fig. 6. The naturalist's dredge. 



1 Rapports et Proces-Verbau.v ; Conseil Perm. Internat. Exploration de la Mer, 

 Vol. VI., 1906. 



- F. Nansen, Publications de Circoiistance , Conseil Perm. Internat. Exploration 

 de la Mer, No. 34, 1906, Copenhagen. The action of these machines is very 

 interesting and well worth study by the reader. 



