NERITIC AND OCEANIC 191 



of smaller size, take a glass tube, about 8 inches long 

 and -| inch outside diameter, hold this between thumb 

 and middle finger, stopping the upper end firmly with 

 the first finger ; lower it thus over the animal, remove 

 the first finger, and animal and water will rush up into 

 the tube. Replace the finger, and the tube with its 

 contents can be lifted out if kept vertical. The 

 animals can thus be transferred to glass dishes and ex- 

 amined, or preserved for future study (see Chapter XL). 



In temperate climates most planktonic animals will 

 live for some time in a glass bottle if absolutely clean 

 and kept cool. In the tropics, where the bottle cannot 

 be kept cool, they die very soon, and should be pre- 

 served as soon as possible. 



For immediate examination on board, as a ship is 

 rarely still enough (except in harbour) to allow of the 

 use of a microscope, a small " dissecting microscope," 

 with simple lenses magnifying about 6 and 10 

 diameters, is absolutely invaluable. 



Naturally enough, the animals in Plankton are not 

 always and everywhere the same. In the first place 

 the distance from shore makes a great difference. 

 Plankton from shallow water near land shows numerous 

 larvae of bottom animals, and such jelly-fish as are 

 budded from hydroids, but over deep water such 

 larvae are hardly ever present ; there are larvae of 

 planktonic adults, but they are not so numerous in 

 proportion, and these adults are mostly different from 

 those near shore. Hence we distinguish the " neritic," 

 or coast-wise Plankton, from the " oceanic," or blue- 

 water Plankton ; the 100-fathom line may be roughly 

 taken as the boundary between them, but they pass 

 imperceptibly into one another. Secondly, the tem- 

 perature of the water makes a great difference in the 

 Plankton ; it is fairly obvious that as a rule an animal 



