METHODS OF OCEANOGRAPHICAL RESEARCH 263 



By the means described above all sorts of animals may- 

 be captured for examination, but the instruments used 

 cannot be said to be quantitative ; they will not supply 

 accurate information as to the abundance of the animals 

 on the sea floor. 



For this latter purpose an instrument known as the 

 " grab " has been made. This is essentially the same as 

 a coal-grab and is constructed so that when it strikes the 

 bottom it literally bites out a piece of the sea bed. The 

 instrument is very heavy, and consists of two hinged jaws 

 which are open as it sinks to the bottom ; on striking the 

 gravel or mud the jaws sink in under their weight, and as 

 the grab is hauled up they are pulled together so that a 

 solid sample of the sea floor is retained (Plate 95). The 

 sample is then sifted through a series of graded sieves and 

 the sand and mud washed away. All the animals remain- 

 ing in the sieve can be picked out and counted and so a 

 knowledge of the population on a definite area of the sea 

 floor is gained. Recently it has been shown that this 

 grab or bottom-sampler is not completely efficient for 

 studying life on hard sandy bottoms as owing to the firm 

 consistency of the sand the grab does not sink deep enough 

 and so fails to catch many of the creatures that live in their 

 burrows a few inches below the surface. To meet this 

 difficulty a new instrument has now been invented which 

 possesses a pump which is put into action just when hauling- 

 in commences. Until the pump has finished its work 

 however the whole machine cannot be lifted off the bottom. 

 The pump is operated by a wire running over a pulley 

 wheel, and until all the wire is pulled off no strain comes 

 on the instrument itself. With the suction set up by the 

 pump the sampler sucks its way into the sand down to 

 a depth of just over a foot, and so a sample of known area 

 and depth is procured. On a similar principle is a little 



