16 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



very different in quantity from a sample taken under the 

 same conditions next day. 



I stopped this series of observations on September 

 17th. After a few days of wind a spell of quiet, calm 

 weather followed, during which I took some tow-nettings 

 both inside Port Erin Bay and outside, both in the day and 

 at night, and all of these differed entirely in character from 

 the gatherings of the previous weeks — being composed 

 mainly of Chceioceros and other Diatoms. During this 

 period of calms and light Easterly winds the surface of 

 the sea was smooth and the water was distinctly coloured 

 by the abundance of diatoms. When the weather broke 

 again, at the end of September, another abrupt change 

 took place, and gatherings taken at the beginning of 

 October showed very few diatoms and many Copepoda. 

 It is evident that if any observer had been taking 

 quarterly or even monthly samples of the plankton in that 

 sea-area he would have obtained very different results, 

 according to the exact date of his visit. On three 

 successive weeks at the end of September he might have 

 found evidence for as many different far-reaching views 

 as to the composition of the plankton in that part of the 

 Irish Sea. How it can be supposed that hauls taken miles 

 apart and repeated only at intervals of months, or even 

 weeks, can give any sure foundation for calculations as to 

 the population of wide sea areas, I fail to see. You must 

 not suppose, however, that I fail to appreciate the 

 labours of the plankton school at Kiel, or that I am at all 

 hopeless as to science attaining to a more exact knowledge 

 of the populations of the oceans. I consider that the 

 leading idea is a good one, that the implements devised 

 are very ingenious, and that the long-continued laborious 

 computations of some of the German professors have been 

 most praiseworthy, But I regard the method as still open 



