SOME PROBLEMS OF THE SEA. 13 



many times another, and the greatest about 30 times 

 as mnch as the least. Now, if a vessel taking observations, 

 say, 20 miles apart, were to have traversed this area and 

 obtained only one of these gatherings, she might have gone 

 off with a so-called sample which was ten or twenty times 

 too great or too small to represent fairly the average, in 

 either case giving an indication that was false and might 

 lead to entirely erroneous conclusions. Similarly in the 

 case of Doliolum, Dr. Fowler found an enormous dis- 

 proportion between the amounts of the catch on the 

 different days, even at closely adjacent localities. It is 

 obvious that if the number of Doliolum present in the 

 area were calculated from one of his samples (such as 

 No. 8) the result would be entirely different from that 

 based upon other samples (such as Nos. 24 and 25). Cases 

 of this kind could be multiplied, and have no doubt 

 occurred in the experience of most naturalists who have 

 done much work at sea. And it was the knowledge of 

 such cases that induced me this summer to devote the 

 vacation almost wholly to making successive plankton 

 hauls day after day in a limited area of the open sea off 

 Port Erin, for the purpose of comparing days, nets, and 

 depths with one another. 



I chartered a small steamer, which proved fairly well 

 suited for the purpose, and cruised mainly between Port 

 Erin and the Calf Island. Nearly 80 gatherings were taken 

 in about 40 days, and I used in all five different nets, all 

 made of fine miller's silk. These were : — 



A Hensen closeable net of 200 meshes to the inch ; 



A small Apstein net of 212 meshes to the inch ; 



An open tow-net, weighted, 120 meshes to the inch ; 



An open surface tow-net, 120 meshes to the inch, new ; 



And an open surface tow-net, 120 meshes to the inch, 

 one season old, 



