METABOLISM IN THE SEA 181 



the animals and plants of the plankton in the dif- 

 ferent seas of the world is a department of research 

 closely related to those I have just mentioned. 

 This work was first systematically pursued by the 

 naturalists of the Challenger in the famous expedi- 

 tion of 18726, and has been taken up by every 

 marine exploring expedition of recent times. 

 Such research, purely zoological, embryological, and 

 distributional, is characteristic of the marine investi- 

 gations of Britain, America, France, and Italy more 

 particularly. In Germany the study of the fauna 

 and flora of the sea has been approached from a some- 

 what different standpoint and by different methods. 

 If we might compare the investigation of life in 

 the sea with the study of the population of a great 

 city, these two lines of marine research can be illus- 

 trated rather well. The British and American in- 

 vestigations might be compared with the methods 

 of the census enumerator, whose task it is to 

 identify and record the individual inhabitants, with 

 respect to occupation, locality, etc., or with the 

 " amateur vagrant," or journalist, who searches for 

 curious and interesting types of humanity. But 

 we can also consider a great city more as a polity 

 than a congeries of individuals, however interesting 

 those may be individually, and study the economical 

 relationships and interactions of the different classes 

 of its population. This latter method of investiga- 

 tion may be compared with the plankton studies 

 of a modern school of German biologists. 



