I5 2 POND COMMUNITIES 



vegetation which comes to the surface of the water and the later marsh 

 and swamp vegetation encroach from the sides toward the center. 



Entomostraca do not ordinarily show so clear a succession of species 

 as do other groups and our collections are very incomplete. The follow- 

 ing have been noted: Cladocerans: Ceriodaphnia reticulata Jurine, C. 

 pulchella Sars, and C. quadrangula Muel. from Ponds 52 to 93. 

 Copepods: Cyclops albidus Jurine appears more common throughout 

 the series and C. viridis Jurine is common in the older ones. Diaptomus 

 reighardi Marsh is in the younger ponds and its place is taken by 

 D. leptopus Forbes beginning with Pond 30. Of the ostracods, Cypria 

 exsculpta Fisch. is common throughout the series. Cypridopsis vidua 

 Mull, is common in the semi-temporary ponds. 



I. FATE OF THE PONDS 



In the late stages the pond dries during extreme droughts and passes 

 rapidly from the stage at which it dries occasionally during a dry season 

 to the stage when it dries every season. It is then known as a marsh or 

 swamp, or often vernal marsh or swamp, or summer dry pond. At such 

 a stage it is a land habitat in summer and a water habitat in spring. As 

 the pond bottom is built up higher by the accumulation of peat, and the 

 surrounding ground-water level is lowered by the forces of erosion, the 

 question of what is to become of the pond brings us to a question of great 

 importance in connection with climatic formations. It will become what- 

 ever the surrounding climatic formation may be. If it is forest, directly 

 or indirectly, the pond becomes forest, and if it is steppe the pond be- 

 comes steppe, while if prairie or savanna the pond becomes savanna. 



We have already noticed that the area of study is on the border of 

 the forest and prairie (steppe formations). A pond in the area of study 

 may therefore become prairie or forest. Ponds with sloping sides usually 

 become prairie, and those with steep abrupt banks or shores turn into 

 forest. There is no marked difference between the animal life of the two. 

 Collections made in a series of three prairie ponds which are situated 

 near Wolf Lake, Ind., and which in ecological age may be compared with 

 Ponds 1,7, and 14 of the Lake Michigan series, are almost parallel with 

 the collections from the Lake Michigan ponds. The differences to be 

 noted are that the snail Planorbis trivolvis, which usually occurs in old 

 ponds only, is found in the earliest pond of the prairie pond series, while 

 the snail Vivipara contectoides and the shrimp Palaemonetes paludosus, 

 which usually occur only in streams and small lakes, also occur in the 

 prairie pond series. The presence of the latter two may be explained, how- 

 ever, by the fact that the ponds were once connected with Wolf Lake. 



