194 TRANSACTIONS LIVERPOOL BIOLOGICAL SOC1KTV. 



samples, taken vertically with these two very different 

 nets, of the organisms present in the water between 10 

 and 20 fathoms. After that three ordinary horizontal 

 open tow-nets exactly alike in all respects (size, shape, 

 mesh, age) were put over — one (A) with a weight attached 

 was allowed to sink to a depth of about 10 fathoms, from 

 which it gradually rose as the ship went slowly ahead ; 

 while the other two (B and C), unweighted, remained 

 continuously at or just under the surface and worked side 

 by side like a pair of sharks or porpoises swimming in 

 our w T ake. These two last nets ought, if there is any 

 uniformity whatever in the plankton even in the most 

 limited areas, to give similar results, and of course they 

 did so in many cases. The purpose in taking the two 

 similar surface nettings side by side was to show this, 

 and also to test the reliability of the sample ; for it was 

 usually considered a more valid sample when these two 

 nets agreed in their evidence. Where, under the circum- 

 stances stated above, the gatherings differed notably, 

 there must have been some accident in the working of 

 the nets or some irregularity in the distribution of the 

 plankton, such as, no doubt, will sometimes be 

 encountered when traversing the edge of a swarm of 

 gregarious organisms ; and it is important to get some 

 evidence as to how frequently such accidents or 

 irregularities may be met with. For example, on April 

 2nd, at along-shore Station III, the two surface-nets used 

 together gave 17 c.c. and 42*5 c.c. of material respectively ; 

 on April 9th, at Station I, 2*5 and 8 c.c. respectively ; 

 and on Ajn'il 24th, at Station II, they gave 7 c.c. and 

 15 c.c. respectively. On many occasions, of coarse, they 

 were very similar, and on some almost identical in their 

 catch (see examples given below). Each of these 

 horizontal nets was hauled for 15 minutes. 



