34 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
different characters as they do in the Hebrides, and that 
a Zoo-plankton and a Phyto-plankton do not occur 
simultaneously a few miles apart. In spring or early 
summer in the Irish Sea, as elsewhere, there is an 
enormous Phyto-plankton maximum, which gradually 
dies away and is replaced by the Zoo-plankton which is 
characteristic of the summer months. In September or 
October again Diatoms make their appearance in 
profusion, constituting a second, autumnal, Phyto- 
plankton maximum. The accompanying diagram (fig. 8) 




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shows, €.g., the curve for the total Diatoms in a recent 
year, as given by a very large series of gatherings, 
extending over every month, taken across Port Erin Bay. 
The high points in April and May, and then again, but 
of less duration, in September and October, show the 
influence of the vernal and autumnal Phyto-plankton 
maxima, and the effect would be almost as marked if the 
curve were drawn to represent the total plankton. 
Taking the results of the last three years in Port Erin 
