Introductory 



reading of the thermometer gives a pretty accurate indication of the 

 precise depth at which the net has been. The net remains down 

 usually for fifteen minutes after the opening messenger has been sent 

 down, and is then closed and hauled up. 



There are advantages about the use of a horizontally-towing net as 

 compared with one vertically actuated, in that the supposed depth is 

 more accurately located to within a few fathoms ; and again, that as 

 marine organisms usually move in shoals, a horizontal net is more 

 likely to capture them than a vertical net, which may pass by a 

 moving shoal, although it may capture a large amount of material by 

 passing through a large vertical excursus. 



The chief object of these researches is to determine generally 

 what species are mesoplanktonic and epiplanktonic throughout a 

 portion or the whole of their existence, and to determine as far as 

 is possible the horizontal and vertical distribution of various species, 

 as far as regards their relation to bathymetrical and climatic con- 

 ditions. 



The desideratum of a good and effectively opening and closing net 

 for deep-water work being great, the author and his skipper, Buchan 

 Henry, set to work to devise an apparatus of the kind which should 

 be effective in deep water ; and the instrument which is described 

 briefly has been found to meet all requirements. 



The inability to determine with absolute accuracy the depth at 



which any net, either of vertical or horizontal pattern is working, of 



course renders all real experimental work only approximate in its 



results ; but I think it must be conceded that all open nets — i.e., nets 



which are not designed to open and close by messengers or other 



effective device at the supposed depth — can only be regarded as 



inefficient in any problems of vertical distribution. 1 



1 Professor O. Pettersson attaches a small net to his current meter, so that water 

 samples, temperature, the velocity of the current, and a sample of the plankton of 

 the area can be taken at one and the same time. Though very useful, Professor 

 Pettersson's statement that this is the only accurate test yet devised for taking 

 reliable samples of plankton cannot be supported, the net being an open one with 

 no mechanism for closing. 



