190 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



separated from the larger organisms such as Sagitta, 

 larval Decapods, and adult Copepoda, except perhaps 

 Oithona. The two portions ihus obtained are carefullj 



transferred to graduated tubes, so that they can be each 

 made up to a known bulk with fresh water. The larger 

 organisms are examined first. If the bulk of the catch 

 which is left on the coarse silk sieve is no1 large, then a 

 direct enumeration of the organisms can be made at once 

 by turning the contents of the tube on to a glass plate 

 with a dark background and examining the animals in a 

 good light with a strong hand magnifying glass, or low 

 power of the microscope if necessary. The various species 

 are recorded as the sample is gone over, and the totals 

 are added up at the end of the examination. If the 

 sample to be examined, however, be too large for a direct 

 and complete enumeration, then it is first gone over 

 carefully and the rarer or larger organisms are counted 

 and removed. The remainder are then returned to 

 the graduated tube and are diluted with water to a 

 workable extent. The tube is then thoroughly shaken up 

 so that a complete mixture or dissemination of the 

 organisms through the fluid is effected. A graduated 

 dipping tube about T % of an inch bore, without any 

 contraction at the end and capable of taking up -} of a 

 cubic centimetre, is quickly inserted into the mixture, 

 f c.c. is taken up and is put on a glass slide. In this way 

 at least five similar samples are withdrawn, care being 

 taken to shake up the mixture afresh previous to every 

 fresh dip. The samples thus obtained are then worked 

 over under the microscope and all the species are identified 

 and enumerated. The average of these countings is 

 taken, and this is multiplied by the factor representing 

 the amount of dilution — thus, if the sample is made up to 

 10 cubic centimetres, then the factor will be 50. The 

 same method is employed in estimating the Diatoms and 



