MAIN PATHWAYS AND TENDENCIES 121 



contributions to knowledge have resulted from the 

 investigations which are published in periodicals of 

 the station. 



Limnology. Fresh water stations have been estab- 

 lished at many points in the United States and in 

 other countries in which the fauna of lakes and rivers 

 have been scientifically studied. The pioneer station 

 of this class was established by Zacharias at Plon, 

 Holstein. Investigation of the biology of lakes and 

 rivers is designated Limnology and work of this 

 nature has assumed considerable importance. 



In connection with aquatic observations, there has 

 developed the plankton work, consisting of studies, 

 both qualitative and quantitative, of the minute 

 floating life of waters. 



Certain Recent Tendencies. The development 

 of the experimental method and its wide application 

 in the different departments of zoological investiga- 

 tion is the most characteristic recent tendency of 

 zoology. Zoological investigation has successively 

 advanced from the stage of mere observation to that 

 of comparison and, finally, to the method of experi- 

 mentation. 



The greatest present activity is in some of the 

 more recent offshoots of zoology such as: cytology, 



