262 HENRY b. ward: 



progress, but in case of those articles not accessible, which in 

 the list are designated by a star, it seemed better to make use 

 of such reviews as were at hand in the various journals, or 

 given in brief form on the cards of the Bibliographical Council 

 at Zurich, in order that the cross references might be as com- 

 plete as possible. 



Of course such a bibliography could not reasonably be ex- 

 pected to give all references on some subjects which are in part 

 included so that it is perhaps wise to state more specifically the 

 limits of the work undertaken. With the exception of a single 

 reference to Hensen, the father of plankton methods, a refer- 

 ence indispensable to all work, no mention has been made in- 

 tentionally of any paper except as it deals in part at least with 

 freshwater investigations. Nevertheless, some of the papers 

 not seen may easily be devoted to marine studies even though no 

 reference thereto is contained in the title. The bibliography is 

 also essentially confined to zoological references although some 

 of the important papers on physical, chemical and botanical 

 topics are cited. The papers of this character given are quoted 

 from many sources, yet certainly do not comprehend all of im- 

 portance on these topics. Their inclusion here is justified by 

 their importance and bearing on the general problems of fresh 

 water work, their immediate relation to the studies of certain 

 investigators and localities, or their occurrence in such sources 

 as render them easily accessible to the general student. Under 

 the topics of taxonomy and geographical distribution, also, no 

 effort has been made to collate all possible references; the en- 

 deavor has been rather to include all those papers of general 

 or special interest and those of most immediate importance and 

 accessibility to American students. Undoubtedly there is room 

 here for cousiderable difference of opinion and the special 

 student of a particular group or region will not find this bibli- 

 ography extensive enough for his purposes, but I hope none the 

 ess tha t it may be sufficiently representative to give a succinct and 

 precise idea of the extent of our knowledge as to the distribution 

 and composition of the freshwater life of the globe and the con- 

 ditions under which it is found. In the systematic part greater 



