the lakes tmtil they had entered streams to spavm. Once again 

 only one size group, that of the smaller, irnniature individuals 

 iiiiich had just recently entered the lake, "was present. 



i 



This interpretation of the data permits the .■generalization 

 that sea lampreys, migrating doivnstrearn to the Great Lakes as 

 recently-metanorphosed individuals in the fall, tTinter, and 

 early spring of any given years A and B, may be e:-:pected to 

 return (as matiare individuals) to streams to spaim and die in ■ 



the spring of year C. The shortest possible span of parasitic 

 existence vrauld therefore be from the early spring of year E 

 to the same period in year C; the longest span from the fall ■ 



of year A to the early summer of year C (end of spav/ning migra- 

 tion). I believe that the great range in length and -weight 

 noted for mature spaivning migrants is attributable, at least 

 in part, to this potential variance in the length of the para- 

 sitic existence mthin the time limits previously indicated. 



Djrmond, Hart, and Pritchard (1929) have presented length 

 data for a collection of parasitic sea lampreys taken in the 

 "autumn" in Lake Ontario. Two distinct size groups were present 

 in their material idiich correspond in length distribution to the 

 two groups present in ny material collected in the same season. 

 The authors thought it possible that their smallest size group 

 represented individuals in their first season in the lake and the 

 larger group, individuals in their second season. In this parti- 

 cular interpretation, our data are mutually substantiating. 



- 171; - 



