The Lake and Brook Lainprcys of New York 479 



as the ice melted the superfluous water of all the lakes gradu- 

 ally fouud an exit through the St. I,awrence basin as it had 

 done in pre-glacial times. 



The application of these geological or topographical 

 changes would have the following bearing upon the special 

 subject of this paper. At the present time in the Susquehan- 

 na River, only a few miles to the south of Cayuga Lake, the 

 large sea lampreys are found in the summer or spawning 

 season and the transforming ones in the autumn, and larvae 

 during the entire year, thus showing that even at the present 

 day the large sea lamprey uses the Susquehanna for a spawn- 

 ing ground. The same is true of the Hudson River. 



Now it is believed that while the lakes poured their super- 

 fluous waters southward into the Susquehanna River that the 

 large sea lampreys frequented the lake and its tributaries and 

 found suitable spawning grounds. As the glacier receded 

 and the streams draining the lake into the Susquehanna 

 became shallower and more difficult to ascend and descend, 

 the lakes were less and less and finally no more visited by 

 the spawning lampreys ; and some of the newly transformed 

 ones, finding abundant food in the common fishes which 

 swarmed in the waters, remained and matured in the lakes, 

 and spawned in its tributaries thus completing the entire life- 

 cycle in fresh water. 



It is also possible that as the water courses to the Susque- 

 hanna decreased and those to the Mohawk and Hudson in- 

 creased, the lampreys entered and left the lake through those 

 streams, but ultimately the same result would follow and the 

 forms become isolated in the lakes. 



If it is granted that the presence of the lake lampreys can be 

 satisfactorily accounted for in the way described, it is not dif- 

 ficult to conceive of the diminiution in size and perhaps also 

 of the other modifications, as the great increase of the dorsal 

 ridge in the male ; for it is within human observation that sea 

 animals that have been artificially or naturally isolated from 

 the ocean gradually decrease in size, and that special features 

 may become accentuated or intensified. 



Ithaca, N. Y. 



September, 1893. 



