We must assume then thai the introduction of these 

 forms into Lake Erie was accomplished by migration 

 after the close of the glacial period. Such a migration 

 is not only possible but may well have happened dur- 

 ing the changes in level known to have taken place sub- 

 sequent to the melting of the great ice sheet. Before 

 the ice melted it filled the basins of all the Great Lakes 

 and entirely removed their previous fauna. In the 

 course of the melting a succession of temporary lakes 

 was formed, of varying sizes and with changing out- 

 lets. At first these lakes discharged to the west into 

 the Mississippi River; they next found an outlet to the 

 east through the Mohawk Valley into the Hudson River. 

 Either of these 2 routes is apparently much too long for 

 a successful migration from the ocean into Lake Erie. 

 But at the close of the glacial period during the Cham- 

 plain substage an arm of the ocean extended up the St. 

 Lawrence valley and covered Lakes Ontario and Cham- 

 plain, and was called the "Champlain Sea. " 



At the time Lakes Superior, Michigan, and Huron, 

 the "Nipissing Great Lakes, " were filled with fresh 

 water, there was an outlet through the Ottawa River 

 into this Champlain Sea. A migration up this outlet 

 into what is now Lake Huron would cover only a com- 

 paratively short distance, and was the probable route. 

 At the same time there was a shorter migration south- 

 ward into the Finger Lakes, in which all three of these 

 crustacean genera are found at the present time. 



When found in Lake Ontario, therefore, these 

 Crustacea are "relicts" in the strict sense of the word 

 since they are found in a lake originally salt which 

 has subsequently become fresh. But in Lake Erie they 

 are not real relicts since this has never been a salt- 

 water lake during or after the glacial period. They 

 must therefcffe be regarded as migrants, for which they 

 are all admirably fitted by the possession of peculiar 

 locomotor ability. Once in Lake Huron their passage 

 into the other Great Lakes could be easily accomplished. 



COMPARISON OF LAKE ERIE AND VICTORIA 

 NYANZA MACROPLANKTON 



largest of African lakes, 200 miles long, 130 miles 

 wide, 73 meters deep. Although it lies on the equa- 

 tor, it is elevated enough above sea level to greatly 

 modify its macroplankton and make it temperate 

 rather than tropical. The water, however, is much 

 warmer than that of Lake Erie, the lowest temperature 

 recorded being 73. 3° F. , the highest 81° F. The 

 water is not normally fresh but contains various salts 

 in solution, especially those of magnesium. 



In Victoria Nyanza there have been recorded 2 

 calanids, 2 harpactids, 8 cyclopids, 1 ergasiUd, and 

 31 cladocerans, 44 species in all, of which 8 were 

 not obtained from the lake itself, but within its drain- 

 age area. In the present survey of Lake Erie, there 

 have been recorded 6 calanids, 5 harpactids, 9 cy- 

 clopids, 2 ergasilids, and 54 cladocerans, 76 species 

 in all, of which 8 were not obtained from the lake 

 itself, but within its drainage area. In Victoria 

 Nyanza 1 calanid, 1 harpactid, and 1 cyclopid were 

 endemic while the remaining 41 species were more or 

 less cosmopolitan. In Lake Erie none of the 76 spe- 

 cies was endemic but all were more or less cosmopolitan 

 Among the copepods only 4 cyclopids are common to 

 both lakes, while among the Cladocera 11 species be- 

 longing to 6 genera are found in both lakes. 



MACROPLANKTON AS INTERMEDIATE HOSTS 



Many species of macroplankton are intermediate 

 hosts to the developmental stages of various fish para- 

 sites. Five of the Cyclops species recorded have been 

 experimentally proved to be possible intermediate 

 hosts for a tapeworm of the walleye pike by H. E. 

 Essex (1928). Four of the Cyclop s species, 3 of which 

 were different from the 5 above, have been shown to 

 be possible intermediate hosts for a tapeworm infest- 

 ing the bass, by G. W. Hunter and W. S. Hunter 

 (1928). Bigelow (1922) reported Lept odora as con- 

 taining the immature stages of some trematode, prob- 

 ably a parasite of the "Jumbo Cisco, " since the Lep- 

 todora was eaten by that fish. 



As the present survey of Lake Erie is the first com- 

 prehensive one of any of oiu; American Great Lakes, it 

 becomes of interest to compare its results with those 

 obtained from similar large lakes elsewhere in the 

 world. The African lakes have been examined with 

 most detail, and of them Victoria Nyanza most resem- 

 bles Lake Erie. This is the shallowest as well as the 



172 



