THE FOOD Or FISHES. 147 



bottom. Many species frequent particular depths, 

 some being found at the bottom, others in mid-water, 

 and not a few at the surface ; but the last group, 

 like the others, is by no means constant either in 

 character or time of appearance. At night they are 

 generally more abundant at the surface than during 

 the day, but they are not always found on the same 

 ground where they may have been met with the 

 night before. 



It is also a curious fact that a gathering from the 

 surface is often found to differ from that obtained 

 a foot or so beneath it. Last summer, when at 

 Lochranza with Mr. Murray in the steam yacht 

 Medusa, Professor Herdman and I were out in a 

 row-boat after sunset. He had a tow-net, which was 

 pulled behind the boat and kept about a foot under 

 the surface, while I had what is called the " hand- 

 net " fixed on the end of a short rod with which I 

 held the tip of the net only a few inches under the 

 surface. It was found that the two gatherings were 

 not alike, but differed considerably in the proi:>ortion 

 of species obtained. I have since repeated the 

 experiment at Cumbrae with the same results. The 

 hand-net, that was kept at the surface, contained 

 more larval forms and amphipods than were captured 

 in the tow-net at a foot or so beneath the surface ; 

 and 'when the two gatherings had been put into 

 separate tubes, that obtained at the surface was 

 seen to be much lighter in colour than the other, in 

 consequence of the greater abundance of hyaline 

 larval forms. 



Although some of these surface animals are widely 

 spread in the water, they are often found in shoals 

 here and there, abundantly at one jilace, and all but 

 absent at another, perhaps not 100 yards distant. 

 These shoals consist chiefly of copepods. and can 

 often be traced on the surface by the fishes that 

 follow them, whose noses may frequently be seen 

 in the water gobbling them up and keeping the 

 water in a state of ebullition. If the net be drawn 



