45° 



[Proc. B.N.F.C., 



who has been for the past year carrying out a research on the 

 plankton of Lough Neagh, described the various nets which have 

 been devised to catch the plankton for the purpose of quantitative 

 estimations, and mentioned some of the results of this work. 

 Hensen, for example, was able by determining the number of 

 plaice eggs floating in a certain area of the Baltic Sea to calculate 

 the number of plaice which must have been present in that area 

 to lay the eggs. Since the number of plaice caught by man per 

 annum in the same area was known, it was easy to determine what 

 proportion of the total fish living in that part was annually caught 

 by the fishermen. The study of the plankton has of recent years 

 become very important, and many biological problems, both 

 economic and scientific, are awaiting solution, when the results of 

 detailed research are known. Thus the great question of the food 

 of fishes, and indirectly therefore the food of man, is bound up 

 with the plankton. Many fishes feed directly on these small 

 organisms floating in the water. Other fishes feed on somewhat 

 larger animals, but even these depend indirectly on planktonic 

 life, which forms the last link between the minerals dissolved in 

 the water and the complex organic compounds devoured by the 

 lowest animals. There is a regular " sea-saw " of life, in fact, in 

 the waters, and one could classify the organisms into producers 

 (mostly plants) and consumers. Amongst the microscopic animals 

 there is a continual struggle, the larger and better armed feeding 

 upon the smaller and weaker, and the plankton caught at any time 

 represents, in fact, the results of the conflict. The constitution of 

 the plankton depends, however, in addition to this, on meteoro- 

 logical conditions. We find plankton present in Lough Neagh in 

 great abundance all the year round, but the organisms are by no 

 means the same at different seasons. There are some character- 

 istic Winter forms. Others appear first in Spring, and soon become 

 very abundant and then die off towards Summer. All these inter- 

 esting changes can only be followed by an investigation of the 

 water at regular intervals through a period of at least one year. 



