MARINE BIOLOGICAL STATION AT PORT ERIN. 41 



weather occurs, as it did two years ago at the end of 

 September, the Diatoms may increase enormously, and in 

 such circumstances they seem to be very evenly spread 

 over all parts and to pervade the water to some depth; 

 but that is emphatically not the case with the Copepoda 

 and other constituents of the Plankton, and it was not the 

 case even with the Diatoms during the succeeding year. 

 I have published in a former report an observation 



Fig. 15. — Series of plankton gatherings showing " swarms " of certain 



organisms (Haeckel's " Monotones Plankton"). 



The jars contain mainly Sagitta, Medusae, Zoea, Calanus, and smaller 



Copepoda, going from left to right. 



that showed very definite limitation of a large shoal of 

 crab Zoeas, so that none were present in one net while in 

 another adjacent haul they multiplied several times the 

 bulk of the catch and introduced a new animal in 

 enormous numbers. Had two expeditions taken samples 

 that evening at what might well be considered as the same 

 station, but a few hundred yards apart, they would have 



