318 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
same rate. Early in August one of the two fine surface 
nets was carried away, and on August 6th a new net 
which had not yet been used, but was otherwise exactly 
similar, was brought out to take the place of the lost one, 
with the result that it at once caught about 20 times as 
much as the old net and more than three times as much 
as the “ Pulley” net. The column headed ‘“ New” in 
the table above shows how this increased catching power 
in the new net diminished rapidly from day to day until 
after being used about nine times, on eight days, it 
caught much the same as the old net used at the same 
a New 
Old 
Fic. 15. Comparison of Catches made by Old and New Nets. 
time. The diagram (fig. 15) brings out this diminishing 
difference clearly, and shows the catches in the old net 
~ keeping at a fairly uniform level, while those in the new 
net form a rapidly descending curve. 
Nets thus “age,” or diminish in catching power very 
rapidly; and moreover some types of catch differ very 
much from others in altering the filtration coefficient of 
the net—for example, a net may have its meshes so 
