SEA-FISHERIES LABORATORY. 189 



Ceratium — C. tripos, C. fusus and C. furca — throughout 

 the year is also noted. 



In the Sea Fisheries Laboratory Report for 1892 the 

 great profusion of Diatoms in the spring, and their 

 replacement later on by Copepoda, was drawn attention 

 to. In the Eeports for 1904, 1905 and 1906 there were 

 special articles on the Plankton of the Irish Sea, in which 

 the spring maximum of the Diatoms and other features 

 of the distribution throughout the year were noted. In 

 the 1905 Report, 365 gatherings had been examined, and 

 in the following year (1906) 400 gatherings. These 

 numbers, the largest up to that date, have, however, been 

 more than doubled on the present occasion (1907). 



In these previous accounts we have used the terms 

 ''numerous," "abundant," &c, or the symbols "r" (rare), 

 " c " (common), " fr " (frequent), &c, as is usually done 

 by other investigating authorities ; but this year we have 

 adopted the plan of counting the organisms in a number 

 of samples from each gathering, and of estimating from 

 these the approximate total numbers of each kind of 

 organism present. The exact method employed has been 

 as follows : — 



Method of Estimation. 



After carefully removing pieces of sea-weed and 

 other foreign matters, the sample is thoroughly shaken 

 up and then allowed to stand and settle for a week. In 

 the case of a very small catch, the sample is first 

 transferred to a narrow tube. After standing for a week, 

 a mark is made on the bottle, indicating the exact height 

 occupied by the organisms. The whole sample is then 

 washed through a silk sieve of 36 meshes to the inch, into 

 one of 200 meshes to the inch. By this process the 

 Diatoms, Dinoflagellates and allied minuter organisms, 

 along with the Copepod Nauplii and young Copepoda, are 



o 



