Number 125 July 10, 1922 



OCCASIONAL PAPERS OF THE MUSEUM OF 

 ZOOLOGY 



UNIVERSITY OF MICHIGAN 



Ann Arbor, Michigan Published by the University 



NOTES ON THE LIFE-HISTORY OF THE BROOK 

 LAMPREY, ICHTHYOMYZON UNICOIOR^ 



By Peter Okkelberg 



The brook lampreys live the greater part of their lives in 

 a larval state, the period of adult existence being less than a 

 year. As far as known, metamorphosis usually takes place 

 in late summer or in the fall. At the time of metamorphosis 

 the larvae have reached the adult size and no food is taken 

 subsequent to transformation. After the spawning season, 

 which is usually in April or in May, all the adults die, and 

 consequently only larvae are found during the early summer 

 months. 



Due possibly to the difficulty of obtaining large collections 

 of larvae from one locality at any one time, no one has yet 

 tried to determine the rate of growth in the brook lampreys. 

 Several attempts have been made, however, to determine the 

 duration of the larval period, but so far no uniformity of 

 results have been obtained. This may be due to the small 

 number of specimens often used in making the calculations. 



1 Mr. Carl L. Hubbs has kindly read and criticised the manuscript 

 for this paper. 



