SEA-FISHERIES LABORATORY. 275 



abundant in May and June, and especially in May; that 

 the adult Copepoda go on increasing till August, and, 

 after a drop in September, attain their highest point in 

 October, while the Copepod Nauplii, as might be 

 expected, precede the adults with a peak in June and 

 July, and another in September. 



If we compare this record with those of former years, 

 it will be seen that in the important period of March, 

 April and May the present year is closely similar to '08, 

 and very different from '07 ; in June, July and August it 

 is intermediate between '07 and '08; in September it 

 shows an increase over the two previous years; and 

 finally, in October-December it is very similar to '08. 



The diagram (fig. 6), in addition to the columns 

 indicating monthly averages for the three years 

 separately, shows, in the outer clear areas to the left, an 

 average for the three years taken together in each month, 

 and in the black areas on the right the averages for 

 the two years '08 and '09. 



The record suggests the idea that '07 was an 

 abnormal year. The rises in alternate months (April, 

 June, August and October) seem unnatural, or at least 

 unusual. The two last years ('08 and '09) agree very 

 closely, except in June, when '09 showed far more 

 plankton than '08. If we take a median position between 

 these two, and connect the tops of the '08 columns by one 

 line, and of the '09 columns by another, the resulting 

 curves show a spring maximum culminating in May, 

 sinking to its lowest in August and then rising again to 

 a smaller maximum in September. This, we think, so far 

 as our evidence goes, is probably the usual form of the 

 annual plankton curve for Port Erin Bay, and it may be 

 seen in the black columns (averages of '08 and '09 taken 

 together) of the diagram (fig. 6). 



