540 TRANSACTIONS LIVERPOOL JJIOLOGICAL SOCIETY. 



that this equal distribution is sufficiently exact to allow 

 of relatively small quantities of water being taken as 

 samples of the total production of the area. Amongst 

 applications of the plankton quantitative method, the 

 following are perhaps the chief : — 



1. To estimate the produce of the sea or ocean or 

 any particular area per year, and to compare the produc- 

 tiveness of different regions. 



2. To investigate the dependence of the plankton 

 as a whole, and also of the different organisms, on the 

 hydrographical conditions, such as light intensity, 

 temperature of the water, salt contents, currents, and, at 

 the surface, wind and waves. 



3. To investigate the relations existing between the 

 different plankton organisms themselves, their dependence 

 on one another, and the relation between the " eaters " 

 and the " eaten." 



4. To investigate the reproduction of the various 

 plankton organisms, and of others not planktonic, but 

 whose eggs or larvae are pelagic ; the relations existing 

 between the number of eggs, the number of larvae and 

 the adults, and the length of time occupied in the life 

 history. 



For the purpose of investigating the condition of the 

 plankton on the high seas, the " Humboldt-Stiftung 

 Expedition " already alluded to was fitted out, no doubt 

 stimulated by the results of the English " Challenger " 

 Expedition. Not all the German zoologists were in favour 

 of the object, and Ilaeckel in particular wrote against 

 it (2), arguing that the pelagic organisms were not equally 

 distributed, but that they travelled in swarms, or at least 

 were so irregular in their occurrence that samples taken 

 at some distance from each other would be valueless for 

 a quantitative estimation. He has been answered in detail 



