7. 



1894.] Zoology. 807 



ZOOLOGY. 



On the Vertical Distribution of Pelagic Crustacea in 

 Green Lake, Wisconsin. — Green Lake is the deepest body of 

 water in the State of Wisconsin, having a maximum depth of about 60 

 meters. Because of its great depth it has not only the litoral and pela- 

 gic fauna? of the shallower bodies of water, but also the true abyssal 

 fauna which is characteristic of the deeper lakes. In fact, the crusta- 

 cean fauna of Green Lake is almost identical with that of the great 

 lakes. 



In the deeper waters of Green Lake are found fifteen species of Crus- 

 tacea. Of these, twelve may be fairly considered as belonging pecu- 

 liarly to the deep water fauna. Most of these can be captured in verv 

 large numbers at night by means of the skimming net. During the 

 day, very few are found at the surface, some few never come to the 

 surface, and are only obtained by dredging in the deep water. 



Of course, an open dredge, dropped from the surface to the bottom 

 and then hauled up, will collect from all depths. After a little experi- 

 ence, the collector has no difficulty in distinguishing between pelagic 

 and abyssal species, and can even draw inferences, with a reasonable 

 degree of accuracy, in regard to the general vertical distribution of 

 species. So far as I know, however, very little exact work has been 

 done to determine the vertical limits of the various species. By means 

 of dredges which could be closed at any required depth, it has been 

 found that in the deep sea there is a surface fauna and a deepwater 

 fauna, but that the immediate intermediate region is barren of animal 

 life. According to Agassiz, the surface fauna extends to the depth of 

 200 fathoms, and the bottom fauna is limited to about 60 fathoms. 



Is there a similar condition in the waters of our lakes ? With a view 

 to answering this question, I made some preliminary collections in the 

 summer of 1893. 



I used, for the collections, a vertical dredge, so constructed that it 

 could be closed at any desired depth. The collections upon which this 

 paper is based were made in the latter part of August, at all hours be- 

 tween five o'clock in the morning and nine o'clock at night. Each 

 series included collections for every five meters in depth. Of course, 

 until a much larger number of collections is made, and at different sea- 

 sons of the year, no final conclusions can be drawn. But the results 

 53 " 



