374 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



PLANKTON OF POET ERIN BAT IN 1912. 



As before, the plan of work is to take two horizontal 

 hauls (coarse and fine nets) and one vertical haul on two 

 occasions each week throughout the year — that is, six 

 hauls per week, about 24 per month, and 312 in the year. 

 The twelve months of 1912 are represented by their hauls 

 as follows : — 



Months . . . 



I 



II 



III 



IV 



V 



VI 



VII 



VIII 



IX 



X 



XI 



XII 



No. of Hauls 



24 



24 



24 



27 



27 



21 



27 



27 



33 



19 



25 



21 



The work has thus been carried out for us with great 

 regularity, and the average per month is about 25 hauls. 

 The lowest monthly record is 19 for October, and the 

 highest 33 for September. The high number in the 

 latter month is due to some extra hauls having been 

 taken in addition to the usual programme. 



The upper whole-line curve in fig. 1 shows the total 

 plankton caught in the horizontal tow-nets (coarse and 

 fine added together) in Port Erin Bay during the months 

 of 1912 ; while the lower broken line shows the 

 corresponding curve for the hauls of the vertical net, 

 multiplied by two for the sake of distinctness. 

 Consequently, the scale on the left-hand margin applies 

 only to the upper curve. The positions of the vernal and 

 autumnal maxima are distinctly seen, and also the 

 summer minimum in July and August. 



Neglecting the vertical hauls at the mouth of the 

 Bay, which give much the same result on a smaller scale 

 as the horizontal nets (see fig. 1) but are not directly 

 comparable with them, and treating the coarse and fine 

 nets together as before, we get the following averages for 

 the total plankton, and the number of individuals of the 



