MARINE BIOLOGICAL STATION AT TORT ERIN. 65 



adhering to sand grains in hollows and crevices (fig. 11). 

 It may have been these inconspicuous resting forms that 

 gave rise to the vast swarms of the following day. 



I am not of opinion, as yet, that this difference in 

 the characters of our Amphidinium indicates more than 

 a variation or " form " of the same species — possibly 

 seasonal, or due to age, or nutrition, or some other 

 environmental influence ; and the existence of this 

 variation does not, of course, affect the broad 

 phenomenon of the striking alternation of the two very 

 different kinds of organisms, the Diatoms and the Dino- 

 flagellates, in vast quantities. It is quite possible that 



Pig. 11. Small quiescent Amphidinia adhering to a sand grain. 



the changes of minute life on the beach are even more 

 complicated than we have yet discovered, and that when 

 no coloured patches are visible the sand is occupied by 

 large numbers of ciliate or flagellate Infusoria. In some 

 of our laboratory experiments we have noticed that as 

 the Amphidinia died and disappeared, colourless 

 Infusoria, which would not be visible to the eye in the 

 sand, took their place as the most abundant organisms, 

 but whether this happens also on the beach is not yet 

 known. 



Although it may not be possible yet to give any 

 detailed and precise explanation of the alternation, the 



