Biological Survey — Oswego Watershed 185 



fish would bump into a lamprey. This seemed strange, for 

 chickens are much agitated when they see or hear a hawk. Per- 

 haps this is because in the racial history a hawk in the neighbor- 

 hood practically always meant an attack, while with the lampreys 

 there is only occasionally an attack. In this experiment it was 

 noticed that at night the lampreys were of a considerably lighter 

 tint than in the daytime. That is, in the day time the pigment 

 cells seemed to be spread out more evenly, and gave therefore a 

 darker appearance. 



As stated, ordinarily the lampreys and the fish swam around 

 together without apparently noticing one another. When, how- 

 ever, a lamprey felt the need of a free meal he would swim along 

 near a fish as usual, and then suddenly with a side movement, 

 the sucking mouth was brought up against the body of the fish 

 and stuck fast. Great excitment followed. The fish Avould dash 

 around the bathtub as if bewitched, and run up the sloping end 

 of the tub almost out of the water. But it was of no use; the 

 harder the fish tore around the tighter the lamprey stuck. 



After several minutes the fish seemed exhausted and thoroughly 

 discouraged and remained rather quiet. On watching the lamprey 

 it seemed to be working hard to get something from the fish. The 

 movements of its head and body reminded one of the actions of 

 a suckling pig or kitten. After some especially hard suck the fish 

 would jump and struggle as if it hurt, It probably did, for when 

 the lamprey let go or was taken off there was always an ugly 

 hole rasped in the fish. 



I saw many attachments, and found that the lamprey could 

 hold fast in almost any position, although a favorite position was 

 near one of the fins. Sometimes the attachment was over the eye. 

 In that case the rasping tongue would dig the eye out, This 

 happened in several instances. The lamprey could change the 

 position of its sucking mouth without letting go. This was strik- 

 ingly shown in a fully scaled carp. The lamprey apparently did 

 not strike a good blood supply when it drilled the first well, so 

 it slid along and dug another so that there were two ragged holes 

 only a short distance apart. 



Besides the above, these experiments Avere carried on to settle 

 the following points : 



Does the lamprey always kill the fish it preys upon? 



How long does a lamprey remain attached to a single fish? 



How often does a lamprey need a full dinner? 



What is the nature of their food? 



How much blood is required for a full meal? 



(a) In answer to the first point, it was found that if the fish was 

 relatively large, the lamprey does not usually kill it, but if the fish 

 is small, the lamprey may kill it. Several examples with large 

 and with small fish showed this over and over. 



(b) It was shown by repeated observations that when a lamprey 

 was fully satisfied, it would let go of the fish. In one especially sat- 



