PREFACE TO THE REPORT OF 1884 ON THE CLADO- 

 CERA AND COPEPODA OF MINNESOTA. 



In presenting what may be denominated a final report of the work 

 done in this state upon the group of Crustacea best represented and, 

 all things considered, most important, the author must admit that the 

 term ''final" refers only to his own opportunities and the limitation 

 of time imposed by circumstances. 



While a comparatively large proportion of all the species existing 

 within our limits have been examined during the progress of these 

 investigations, there undoubtedly remain many additional and curious 

 forms to reward the search of the student. A great variation in the 

 degree of completeness with which tbe different genera and sj)ecies 

 have been treated will be observed, due in part to the circumstances 

 under which they were studied and frequently to the poverty of ma- 

 terial. The entomostracean fauna is quite different at different sea- 

 sons, and a complete knowledge of even our local fauna requires a long 

 period of observation. Even the dead of winter is a favorable time to 

 study some groups. The late autumn is, perhaps, the most favorablf^ 

 opportunity; for then, in one group, the sexual activities are just at 

 their height and both sexes may be studied. A number of Cladocera 

 are restricted to this season. There are a number (how large it is not 

 yet possible to tell) of species in both groups which are to be sought 

 by night, though no phosphorescent species are yet known. Our 

 larger and, especially, deeper lakes have a quite different fauna from 

 the shallow pools and rivers. In general, the flowing waters are poor 

 in Entomostraca. The Cladocera or shelled Eutomostraca have here 

 received a large share of attention, and more particularly the Lyn- 

 ceid?e, which are the most minute of Arthropods. This study has been 

 rewarded with an unexpectedly large number of forms, and a particu- 

 larly large number of species identical with those of Europe and else- 

 where. Professor Birge is the only American M^-iter who has 

 attempted this group, and his valuable work has made us familiar 

 with the more striking new species. A few new species are included 

 in our list and several varieties hirdly yet known in Europe. The 



