THE PLANKTON 329 



pound honey jar, while another requires two seven-pound fruit 

 jars to contain it. 



The size of a catch, of course, depends upon various factors, 

 such as the size of the net, the time it was fishing, or the amount 

 of water passing through it, and the quantity of plankton in the 

 sea at the place where the haul was obtained. 



A small number of sea-water samples were collected from 

 various depths by means of the Nansen-Pattersson water-bottle. 

 These were generally taken from the areas in which plankton 

 samples were obtained. The object of these water samples is to 

 ascertain the salinity of the sea at different points and at differ- 

 ent depths. 



Any change in the salinity means a marked change in the 

 character of the plankton. 



The plankton catches, when sorted, will doubtless be found 

 to contain many new genera and species to add to the list of the 

 known forms of living things. The vertical hauls, which were 

 generally made for quantitative purposes, will help to increase 

 our knowledge of the relative abundance of the plankton over 

 the oceans of the world and at different seasons of the year. 

 Isolated observations such as these may be of small value in 

 themselves, but every expedition which collects such data thereby 

 adds its quota to the gradually accumulating mass of evidence 

 and brings the time for generalisation nearer to hand. A knowl- 

 edge of the relative abundance of the food supply of the ocean 

 is not only of scientific interest but of commercial importance. 



On the homeward voyage two satisfactory hauls with the 

 trawl were obtained, one off the Falkland Islands in a depth of 

 125 fathoms, and the other off Rio de Janeiro in 40 fathoms. 

 The trawl scrapes the bottom of the sea, and brings up a fair 

 sample of whatever animals and plants it can entrap or uproot. 



So little scientific trawling has been done in the Southern 

 Hemisphere that almost every haul has a chance of containing 

 some creature hitherto unknown from the area in which the catch 

 was obtained. 



Animals which live at the bottom of the sea are known to 

 zoologists as the benthos. 



During the outward voyage a day was spent on the island of 

 South Trinidad by several members of the Expedition, and col- 



