Article I. — Plankton Studies. I. Methods and Apparatus in 

 Use in Plankton Investigations at the Biological Experi- 

 ment Station of the University of Illinois. By C. A. Kofoid. 



Less than ten years ago a new field of biological science 

 was opened by the German investigator Hensen, namely, the 

 quantitative examination of the " Plankton." This term was 

 applied to all plants and animals floating free in the water 

 and incapable by their own efforts of materially changing 

 their position. Thus adult fish which brave the waves and 

 stem the current would not be included in the plankton, 

 while the passive eggs or the helpless fry would fall within 

 the limits of the definition. Practically, the content of the 

 term plankton as applied to fresh water is the sum total 

 of its minute life, both plant and animal. 



The scope of our plankton work upon the Illinois River and 

 its adjacent waters includes a continuous, systematic, and 

 exhaustive examination of the plant and animal life sus- 

 pended in the waters of a river system, with a view to deter- 

 mining its amount and seasonal changes, its local and vertical 

 distribution, its movement and relation to the current, the 

 effect upon it of floods and of drouth, of light and of tempera- 

 ture, the organisms which compose it, their seasonal and 

 cyclic changes, and their mutual interrelations. Added 

 interest arises from the fact that this is the first application 

 of this method of biological investigation to a river system 

 and its related waters. 



It is the purpose of the present paper to describe the 

 methods and apparatus employed in the plankton work at the 

 Biological Station at Havana, Illinois, during the years 1894- 

 1896. Both are, as a rule, the result of mutual conference 

 of the various members of its staff. During the first 

 fifteen months of the existence of the Station the plankton 

 work was in the hands of Professor Frank Smith, and when, 

 on July 1, 1895, the writer assumed charge of this work at 

 the Station he found the oblique haul, described on a subse- 



