SEA-FISHERIES LABORATORY 



2m 



whole the Copepod Nauplii increase to a maximum on April 

 17th, when they are exceptionally numerous (see Form 

 36), and then fall off, so that the numbers at the end of 

 the month are much the same as those at the beginning 

 of the period under observation. 



It is clear then that the problem of the periodic 

 distribution of these various organisms is not quite so 

 simple as might have been expected. There are probably 

 three distinct factors at work: — (1) the periodicity of the 

 stages in the normal life-history of the organism ; 

 (2) irregularities introduced bv the inter-action of the 



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organisms, as when one group serves as food, or enemy 

 of another ; and (3) abnormalities as to either time or 

 abundance caused by weather conditions, which may 

 either prevent the normal or permit of an abnormal 

 development of certain species. 



Mr. Laurie has kindly drawn for us the accom- 

 panying curve (fig. 9) representing our results as to the 

 Diatoms in the bay compared with those from the open 



sea. 



