No. 552] 



THE SEA LAMPREY 



mouth and carried out. Larger stones, firmly rooted in 

 the bottom, require considerable effort to be dislodged; 

 the stone is tugged upward, the lamprey receding back- 

 ward in a straight line. Sometimes instead of pulling 

 backward, the lamprey charges head-on and pushes the 

 stone in front of it up the incline, the body remaining 

 rigid and acting as a lever, while the tail is lashed vio- 



lently to gain a firmer support. Some of the larger 

 stones carried by the lampreys out of the nest (Fig. 4), 

 were picked up just as they were released from the 

 mouth; they were found to weigh (in air) from 145 to 

 840 grams. 



The building and improving of the nest go on continu- 

 ously between intervals of mating. Both the male and 

 the "female take part in this work. On one nest there 

 were observed a male and a female ; they were joined now 

 and then, for some minutes, by a second female which 



