164 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY 



the percentage deviation from the average of each series is in 

 no case great. The volumes of these series are as follows : — 



Average. 



April 8— 0-6, 



0-6, 0-5, 



0-5, 



0-4, 



0-5. 



... 0-52 c.c. 



„ 13— 0-4, 



0-6, 0-5, 



0-4, 



05 





... 0-48 c.c. 



Mav 25—19-5, 



15-0, 15-5, 



14-5 







.. 16-125 c.c 



Sept. 16— 6-2, 



7-5, 4-5, 



6-2 







6-10 c.c. 



If, however, we examine the detailed results of the micro- 

 scopic investigation of the catches, we find that even in the same 

 series similar volumes of catches may be made up rather 

 differently, and may in some cases show surprising differences 

 in the numbers of a species in successive hauls, such as 10 and 

 100, 40 and 800, 4,000 and 18,000. The same organisms are 

 present for the most part in each haul of a series, and the 

 chief groups of organisms are present in much the same propor- 

 tion. For example, in a series where the Copepoda average 

 about 100, the Dinoflagellates average about 300 and the 

 Diatoms about 8,000. On another occasion we find Copepoda 

 about 1,000, Dinoflagellates about 4,000 and Diatoms about 

 100,000. These are in mixed catches ; in a phytoplankton 

 (May 25th) the Copepoda may be in hundreds, the Dinoflagel- 

 lates in tens of thousands and the Diatoms in the millions. 

 But notwithstanding this appearance of similarity between 

 the hauls of a series, there is a considerable percentage deviation 

 in the case of some hauls from the average of their series — not 

 infrequently about plus or minus 50 per cent., in several cases 

 about 70 and in one case plus 129. The following table gives 

 the percentage deviations in the case of the volumes, and of 

 the estimated numbers of the four chief groups of organisms 

 present, viz., Diatoms, Dinoflagellates, Copepoda and the 

 Nauplii of Copepoda. 



In all there are about 50 species of organisms that occur 

 with fair regularity throughout the series : 24 species of 

 Diatoms, 4 of Dinoflagellates, 8 of Copepoda and about 14 other 

 organisms or groups of organisms which are not of so much 



