168 Wisco7isin Academy of Sciences, Arts, and Letters. 



timated bef ore, it is of great practical interest in connection with 

 the problems of fish culture. It may not be likely that, as sug- 

 gested hy a recent writer in Forest and Stream^ the future 

 angler Avill carry with him a thermometer and chart with a 

 statement of the laws of vertical and horizontal distribution, 

 but such study does give a fundamental knowledge which is of 

 vast importance to the angler as well as to the fish culturist. 



The terminology used in the study of the fauna and flora of 

 fresh-water lakes, as in the sea, was formulated by Hackel. 

 Under the term ^'plankton" is included all living things, animal 

 or vegetable, found in the water which do not move from place 

 to place by their own volition. Fishes are not considered a part 

 of the plankton. The life of the sea may be considered as ^'lit- 

 toral," "i^elagic,'' and "abyssal." To these terms Hackel adds 

 "zonary", to include those animals Avhich are supposed to occur 

 at zones of different depths in the ocean. In the littoral and 

 pelagic planktons Vv'e may have both animals and plants, but in 

 the abyssal no plants are found except bacteria. The study of 

 the pelagic and abyssal faunas has been entirely within the last 

 half century ; in fact the very knowledge of their existence dates 

 back hardly fifty years. 



In the lakes we use a similar set of terms. The regions are 

 "littoral," "limnetic," and "abvssal." The characteristics of 

 these regions are somewhat known, but still our knowledge is far 

 from perfect. 



A list of the plants and animals found in any one lake seems 

 quite formidable because of its length, but the species that are 

 present in any considerable numbers are very few. From a lim- 

 netic collection, for instance, we may find in abundance the fol- 

 lowing: four or five copepods, five or six cladocera, three or 

 four protozoa, and perhaps two rotifers. This would be a fair 

 average fauna in one of our lakes. Of the plants, we would find 

 two or three diatoms and as many alg'^e. 



^ot only are the anin^als and plants of neighboring lakes 

 very much alike, but the same animals may be found distributed 

 over wide territories, and even over different continents. This 

 is true even of some of the higher animals of the plankton, like 

 the crust,acea. Of our fifteen species of Cyclops nine are found 



