silvery-vdiite ventrally in the transformed individual; and^ (I4) 

 the height of both dorsal fins becomes more pronoiinced. I have 

 taken sea lampreys in advanced stages of transformation (for 

 the external characters described) in larval beds in the Ocqueoc 

 River' during the latter half of the month of August. No such 

 individuals were found in collections made during May and June. 

 I deduce from this that some individuals probably begin the 

 metamorphosis of these externally visible characters as early as 

 the July preceding the winter when they will leave the silt beds. 

 Transforming individuals were taken in all collections made from 

 October to January; iiith each succeeding month of this period 

 the frequency of their occurrence increased. 



As early as October 1? (in 19hl), I collected several sea 



lampreys from a silt bed which;, on gross examination., appeared 

 completely transformed; subsequently, additional individuals in 

 this condition were talcen from burrows. These data suggest that 

 the metamorphosis of gross external features requires at least 

 three and one-half months during vdiich it is highly unlilcely that 

 the indiiddual is capable of feeding, I do not Icnow v^rhether the 

 onset of internal changes precedes the visible external changes 

 in the sea lamprey. Should this occur, then it is likely that 

 the minimum period of metamorphosis and the period T±ien no feed- 

 ing takes place would be of greater duration. 



IX. Downstream movement of r e cently-trans formed adults 



Methods of study 



At the inception of these investigations, some uncertainty 

 existed as to precisely when the doTmstream movement of recently- 

 transformed, adult sea lampreys occurred. Furthermore, ecological 

 factors irifluencing these movements were unknown. Occasional field 

 observations and studies of larval populations suggested that this 

 movement took place during the winter and/or spring months. In 

 order to obtain more precise information as to this plriase of the 

 sea lair.prey's life cycle, two trapping devices of radically differ- 

 ent design were operated in the Ocqueoc River, Presque Isle County, 

 and the Carp Lake River j Bmnet Coxmty, during 19U8 and 191+9. 



(1) The Ocqueoc River weir and trap for newly 



transformed lampreys 



A description of the design of the Ocqueoc River weir and 

 traps has been presented in a preceding section (Pages 28-30). 

 In order tc trap the young sea lampreys moving downstream, framed 

 sections of 3/l6--inch mesh screen (hardware cloth) were set on 

 the iipstream face of the grates of the weir (Figure 57)° Screens 



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