CH. Vl] QUANTITATIVE PLANKTON INVESTIGATIONS 123 



brass screws which can attach the bucket to the net. In the most 

 elaborate nets the bucket is a cylinder made of two parts. The 

 lower part is a copper cylinder, the bottom of which is a short cone 

 terminating in a stop-cock; and the upper part is made of the same 

 silk as the net itself The metal part of the bucket is tinned on 

 the inside and painted on the outside. Sometimes the upper silk 

 part of the bucket is dispensed with and then this part consists 

 only of the metal cylinder and stop-cock. In the figure the more 

 elaborate apparatus is represented. The lower part of the guard 

 is an iron ring which prevents the stop-cock from coming into 

 contact with the mud at the sea bottom when the net is lowered 

 until it touches this. 



The net is made of " Mullergaze " (or hotting cloth), a fabric 

 which is used by millers for separating the various grades of flour. 

 It is made of very fine silk thread and the meshes have various 

 sizes. In fishing for the larger planktonic organisms the coarser 

 cloth is used, but when it is desired to catch the very smallest 

 things in the sea the cloth is selected which has the finest mesh 

 obtainable. The mullergaze used in the vertical Hensen nets is 

 usually that numbered 20 and this has, on the average, about 

 5900 meshes to the square centimetre. The length of side of 

 each mesh is about 0"05 mm., and the area of the mesh is about 

 0*0025 sq. mm. The shape of the mesh is pentagonal and the web 

 is so constructed that the meshes are all very similar and cannot 

 easily be distorted. 



The cloth is cut so that, when the two straight edges are sewn 

 together, the net when opened out has the form of a long truncated 

 cone. The wider end of this cone is 100 cm. in diameter. It is sewn 

 to a piece of canvas and this is attached to the iron ring which 

 forms the base of the headpiece. The smaller end of the net is 20 cm. 

 in diameter and is also attached to a strong piece of cloth which 

 is sewn into a piece of fustian which is folded over a brass ring 

 which screws on to the upper part of the bucket. The net itself 

 is not strong enough to stand the strain of hauling and the bucket 

 is carried by another net made of. strong twine, and having coarse 

 meshes. This net is laced to the base of the headpiece and to the 

 brass ring which forms the lower part of the net. Outside this 

 net again there are a number of ropes which give additional 



