326 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



from 60 to 70 per cent, of animals. One Oopepod equals 

 in dry weight 157 Ceratium individuals, or 1,500 

 Chcetoceros cells. 



In order to illustrate the distribution of the plankton 

 during different months of the year, Brandt has drawn 

 up annual curves for the years 1889 to 1893. The curves 

 are based on the results of over 300 catches taken at a 

 given spot, Buoy A, at the entrance to the Bay of Kiel, 

 and at a depth of 20 metres. These catches were all made 

 by means of the large Hensen plankton net. The curves 

 are volume curves, based on volume measurements after 

 the catch has been allowed to stand for 24 hours. 



Very large catches are only made in the spring (fig. 9), 

 from the middle of March or in April to the beginning of 

 May. These maxima are due to the fact that at this time 

 of the year the Diatoms multiply to an enormous extent, 

 and this is especially true of Chcetoceros. In the summer 

 we get a second increase of Diatoms, namely, of Rhizoso- 

 lenia species, so that in August or September a second 

 maximum is established. The other catches show less 

 marked peculiarities. The minima of plankton produc- 

 tion occur in February or March, and again in May or 

 June, that is, before and after the chief periods of increase 

 of the Diatoms. 



Although Hensen or Brandt made at least 70 observa- 

 tions at this spot, only on one occasion did they find so 

 small a volume as usually occurs in the Sargasso Sea, and 

 that was in February, 1894 (fig. 9). The Diatoms are so 

 extraordinarily prolific that, in spite ol their small size, 

 they play an important part in modifying the plankton 

 curves. 



In conclusion, I may quote, as an example of the far 

 reaching effect of plankton studies, from a highly interest- 

 ing and suggestive work recently published by Brandt (9), 



