866 ON THE FAUNA AND BOTTOM-DEPOSITS NEAK THE :'.0-FM. LINE 



double purpose for which the IMarine Biological Association was 

 founded, namely, to increase our scientific knowledge of marine 

 animals, and to obtain information having a direct bearing upon 

 problems connected with sea-fisheries. It does not, I think, require 

 any elaborate argument to demonstrate what is brought out clearly in 

 detail in the present report, that the inter - relations between the 

 different animals living in one neighbourhood are so intimate and 

 complex that one cannot hope to understand the natural history of 

 any particular group, such as the fishes, without a knowledge of the 

 whole fauna of which that group forms a part. 



Since the principal object of the investigation was to study the 

 relation of the fauna to the bottom - deposit, the area selected for 

 examination was so chosen that the general physical conditions pre- 

 vailing over the whole of it were uniform, and showed no very marked 

 differences in any feature beyond the changes in the nature of the 

 deposits. The hauls were all made at nearly similar depths, the thirty- 

 fathom line being roughly followed from the Eddy stone to Start Point. 

 (See Charts I.-XVl.) Probably the only variable factor which is of 

 any importance at all, in addition to the bottom-deposit, is the amount 

 of disturbance of the bottom water due to the action of waves, which 

 is discussed on p. 375. 



On the western portion of the area the Eddystone Lighthouse, stand- 

 ing as it does upon a reef which rises abruptly with water of thirty 

 fathoms depth all round it, forms a valuable landmark, and enables one 

 to determine without much difficulty the positions of the difl'ereut 

 stations. 



The instrument used in making the collections has been for the 

 most part an ordinary naturalist's dredge, the mouth of which was from 

 2 ft. 6 in. to 3 ft. long and 6 to 8 inches deep. On the finer grounds 

 a small otter-trawl and a small beam-trawl (27 ft. beam) have also been 

 employed. For obtaining actual samples of the bottom - deposits a 

 dredge fitted with a canvas bag inside the ordinary net was used. 



About 100 hauls of the dredge or trawl were made altogether, and so 

 far as practicable every species captured was identified and recorded, 

 note being made of its relative abundance, and in the case of fixed 

 species, of the objects to which the specimens were generally attached. 

 It was afterwards found possible to group together many of these hauls, 

 which having been made close to one another showed a similar fauna 

 and bottom-deposit, and these groups have been called grounds. In 

 all eighteen grounds have been recognised. 



As already stated, the investigation was commenced in 1895, and it 

 was continued each year till 1898, the hauls having been made at 

 different seasons, but for the most part during the summer. At these 



