320 henry b. ward: 



by Forbes (94, 97) and the particular problems with which one 

 has to deal in such a location. Under the direction of the 

 same investigator there has been opened on the Illinois River 

 a station which is devoted primarily to the problems of a river 

 system. Some of the results are given in the papers of Hart, 

 Hempel and Kofoid. Lauterborn (93, 94) and others have 

 done some work on the fauna of a river, and recently the topic 

 has received more attention. Schroder (97a, 98a) finds in rivers 

 the phytoplankton much in excess, the diatoms constituting the 

 ruling forms. In shallow ponds with not too strong an inflow 

 the zooplankton is far richer than in streams where it decreases 

 with increasing current. Zacharias (98a) shows that the potanio- 

 plankton is formed in plant-grown bays on the river shore, and 

 multiplies perhaps in slow-flowing streams. Zimmer (98) finds 

 that the character of the potamoplankton varies with the hight 

 of the water. He distinguishes (1) autopotamic forms which 

 find their conditions of existence only in flowing water. These 

 include at most very few animals. (2) Eupotamic f orms, living 

 either in standing or flowing water, including most species of 

 the river plankton. (3) Tychopotamic forms, torn by chance 

 from quiet waters in which they live normally, and finding no 

 possibility of reproduction in the current. The potamoplank- 

 ton is very poor both in species and individuals as compared 

 with the limnoplankton. The Rotatoria constitute its chief 

 element, adult Crustacea are rare, and only one protozoon has 

 been observed. It is interesting to note that in a lake of the 

 Jura, Zschokke (94) records that the variations of level and the 

 strong current give it partly the character of a river. Here 

 the littoral zone is almost barren but the limnetic fauna rich 

 in species though poor in number of individuals. 



No specific report is on record during this period concerning 

 the investigation of a swamp. The closest resemblance to 

 such conditions are presented by Lake Nurmijarvi (Stenroos, 

 98) which possesses in fact a maximum depth of one meter. 

 Here could be distinguished nevertheless the characteristic re- 

 gions of the pond or lake fauna. The extreme richness of such 



