MARINE BIOLOGICAL STATION AT PORT ERIX. 51 



plankton silk (No. 20), still so mucli clogging of the 

 meshes always takes place in such hauls, and so many 

 other smaller organisms and particles of mud are 

 retained, that it is certain that had the Amphidinium 

 been present in any quantity in the water it would have 

 shown up in the gatherings. 



" Careful scraping of the sand showed that the 

 Dinoflagellates were only in and on the surface-layer, 

 and therefore could not be regarded as coming up from 

 below. It occurred to us that possibly they might be 

 fresh-water forms derived from the land ; but we 

 ascertained that the little stream in the centre of the 

 bay, which in wet weather overflows on to the beach (at 

 other times it is conveyed into the town sewer), had not, 

 on account of the unusually diy season, sent any water 

 to the beach for some weeks. Moreover, on experimenting 

 with the living Amphidinium in the laboratory, Miss 

 Latarche found that while it lived well in sea-water, or 

 when diluted with a little fresh, it died at once in fresh 

 and survived for a few days only in brackish water, 

 containing only a little sea-water. The exact salinities 

 of these mixtures were, unfortunately, not noted at the 

 time. Samples of the Amphidinium kept in shallow 

 dishes of wet sand at the Biological Station in a few 

 days showed such profuse growth that the sand was 

 covered by a dark-coloured layer, the water became 

 impure, and eventually all the Dinoflagellates died off. 



" Observation under the microscope shows that 

 although this is a singularly active Dinoflagellate, 

 circling round and round with great vigour, so that a 

 drop of sand and water containing a number of the 

 organisms presents a most animated picture under a low 

 power magnification, still the Amphidinium seems to be 

 actually attracted to the sand-grains and associated with 



