LINNEAN SOCIETY OF LONDON. 27 



wise to secure by detailed local work a firm foundation upon which 

 to build, and to ascertain more accurately the representative vahie 

 of our samples before we base conclusions upon them. 



I do not doubt that in limited, circumscribed areas of ^^ate^, in 

 the case of organisms that reproduce with great rapidity, the 

 plankton becomes moi*e uniforml}- distributed, and a comparatively 

 small number of samples may then be fairly representative of the 

 whole. That is probably more or less the case with fresh-water 

 lakes ; and I have noticed it in Port Erin Bay in the case of 

 Diatoms. In spring, and again in autumn, when suitable weather 

 occurs, as it did last year at the end of September, the Diatoms 

 may increase enormously, and under such circumstances they seem 

 to be very evenly spread over all parts and to pervade the water 

 at all depths ; but that is emphatically not the case with the Cope- 

 poda and other constituents of the plankton, and it was not the 

 case even with the Diatoms during the present spring. 



With the view of testing plankton methods still further, at 

 another time of year, I devoted a month this spring (March 28th 

 to April 27th) to a systematic exploration, from the S.T. ' Lady- 

 bird,' of the sea off Port Erin at the south-west corner of the Isle 

 of Man. The region in which I worked measured (see map) 



10 miles from east to west (out to sea) and rather less from nortli 

 to south (along the coast), but the area investigated was really 

 much more limited than these numbers indicate, since the samples 

 were taken from only two " off-shore " stations, one 5 miles (I.) 

 and the other 10 miles (II.) out from Bradda Head ; and frona 

 three " along-shore " stations, one to the north (III.) tov ards 

 Niarbyl, one to the south (IV.) towards the Calf Island, and 

 one in the "southern sea" (Y.) off Spanish Head — all in water 

 of much th<^' same depth, about 20 fatlioms. 



