DISTRIBUTION OF SPECIES. (57 



the conditions of water are more stable than those of the land, 

 there will he, in some ways, greater variability in the annual 

 productiveness of the water. The changes in the vegetation, 

 will have a greater or less influence in controlling the animals, 

 but in some cases, the animals seem to 1 grow almost independ- 

 ently of the plants. 



Examples of this apparently erratic production are seen in 

 the comparison of the Gloiotricliia curves in Lake Winnebago 

 in the summers of 1899 and 1900, and in animals in the Diap- 

 tomus curve of 1901 in Lake Winnebago as compared with that 

 of the preceding years, or the Diaphanosoma curve of 1899 as 

 compared with the succeeding years. 



It is apparent that the balance of life is maintained much 

 more evenly in deep lakes than in those that are shallower. 



It is to be noticed, too, that in the shallow lakes there is al- 

 ways an overproduction of plants in the summer as compared 

 with the animals. This has been remarked by many other 

 authors. The overproduction becomes so great at some times 

 in mid-summer that the water through the decay of the plante 

 may become actually poisonous to the fish. 



!; 



RELATIVE VALUE OF DEEP AND SHALLOW LAKES FOR THE PRO- 

 DUCTION OF FISH. 



If lakes are to be ranked for fish production in accordance 

 with their amount of plankton, the shallow lakes must be con- 

 sidered vastly the most valuable. As has been stated before, 

 this is generally considered to be the fact. It seems to me, how- 

 ever, that this difference, if it exists, has been much overstated. 

 Fish are dependent for their food, for the most part, on the 

 animal part of the plankton, not on the plants. It is the ento- 

 mostraca that furnish the basis of food for fishes. ISTow, in 

 Groor: lake the entomostraca are not only more numerous than 

 in Lake Winnebago relatively to the plants, but are also abso- 

 lutely more numerous. They are at least as numerous in the 

 summer, and during the winter there is a considerable produc- 



