bb TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



facts seem to point to the probability that the cause of 

 the phenomenon is a physiological one, and that the 

 explanation may consist in showing that each organism 

 in turn, in its life-processes or metabolism, exhausts or 

 alters some essential constituent of the environment, so 

 as to prevent its own continued existence, in quantity, 

 at that spot, but leaves the ground suitable, or even 

 favourable, to the physiological needs of the other set of 

 competing organisms. 



Possibly we have a similar phenomenon on a more 

 extended scale in the now well-known seasonal and other 

 variations in the plankton of the open sea, where during 

 spring and summer, as we have shown by our work at 

 Port Erin, the main constituent groups of organisms are 

 Diatoms, Dinoflagellates, and Copepoda, succeeding one 

 another in that order. Figures 12 and 15 on page 70 

 show a spring gathering of phyto-plankton (Diatoms) and 

 a summer gathering of zoo-plankton (Copepoda), as seen 

 under the microscope. Figure 13 represents the inter- 

 mediate group, Dinoflagellata (to which Amphidinium 

 also belongs). 



In this connection it is interesting to see that 

 Professor Benjamin Moore has recently discovered, in 

 the course of his Percy Sladen Trust research at Port 

 Erin into the Nutrition of Marine Animals, that there is 

 a notable change in the chemical reactions of the sea- 

 water round our coasts at different seasons of the year — 

 no doubt in co-relation with the development of vast 

 quantities of plankton organisms. In spring (April) the 

 water, not only on the shore but also out in the open 

 sea, is acid to phenol-phthalein, while in summer 

 (August) it is distinctly alkaline to the same indicator. 

 This change signifies an enormous conversion of carbon 

 in the inorganic into carbon in the organic form— a 



