44 



TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY 



organisms should be counted approximately, and the 

 results, in round numbers, may be used in comparing 

 catches or in tracing changes ; but such figures should not 

 be made the basis of calculations as to the total numbers 

 of such organisms in the oceans. In brief, the numerical 

 results of quantitative work should be regarded as giving 

 relative but not absolute information. 

















— -Ci^i."" 'Sr*" ** . 



^r* jj^ ^£ 



^l " S s U ^ 



-1^5 £x 



V ^ *t« 



^t' I ?^<- 



Jp — ± ± k^s 



4 "^x 



+' * 



?, A 



^"5 



C_ _J_ ^jAiinilfi_ 







5*WM^/ *- uS^^^u 



L-'' i,^Au:' 



--.d^ CI ^.- 



=.^-1 H. S 



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i 



Fig. 17. — Diagram showing the influence of the factors C, B, D, 

 upon the life-history A. 



The factors causing the seasonal and other variations 

 in the Plankton already pointed out may be grouped under 

 three heads, as follows : — 



(1) The sequence of the stages in the normal life 

 history of the different organisms. 



(2) Irregularities introduced by the interactions of 

 the different organisms. 



(3) More or less periodic abnormalities in either 

 time or abundance caused by the physical changes in the 

 sea, which may be grouped together as " weather." 



