Manchester Memoirs, Vol. Iviii. (19 14), No. 8. 21 



Though at the time of our investigations we were un- 

 aware of Wesenberg-Luncl's arguments for the use of nets 

 of varying degrees of coarseness, if a fair idea of the nature 

 of the plankton is to be obtained, our experience prove the 

 wisdom of his contention. We have found the contents of 

 the fine and coarse nets, hauled at the same time, to differ 

 very widely, and if we had only used a fine net, our ideas 

 as to the relative abundance of the larger organisms, such 

 as the Crustacea and larger Rotifera, would have been 

 quite erroneous. We suppose that the fine net very 

 rapidly has its meshes choked with small phytoplanktonic 

 organisms, and that, though nominally towed for five 

 minutes, it is actually straining water for a very much 

 less time. After the meshes of the net become choked, the 

 net plus the contained water acts as a solid object pulled 

 through the water, and instead of straining, it merel}- 

 pushes the water aside. In this way the large organisms 

 are not captured, and an erroneous idea of their relative 

 abundance results. 



Although we admit that a vertical haul, in which the 

 organisms are duly counted, conveys the only exact idea 

 of the relative abundance of the planktonic organisms at 

 a given time, we submit that regularly collected surface 

 hauls, with both fine and coarse nets, give a very fair idea 

 of the seasonal changes and periodicity of planktonic 

 organisms. Our surface hauls were made entirely from 

 the qualitative point of view, but, in so far as we have 

 examined them, we believe also that they present an 

 accurate picture of the variations in number and kind 

 of the organisms which constitute the plankton through- 

 out the year. 



