BREEDING 287 



with bruises even before they reach them, and on these injuries 

 patches of deadly fungus are developed; the fins may be 

 mutilated, the eyes injured or destroyed, the gills heavily 

 infested with parasitic worms, and the flesh white from loss of 

 oil. Thus, as soon as the reproductive act is accomplished, 

 sometimes even before, all of them die, and in some rivers the 

 corpses of spent fish may be observed lining the banks for miles, 

 piled, in some cases, to the height of several feet. 



The Sea Lamprey {Petromyzon) will serve as another example 

 of an anadromous fish whose spawning habits are of special 

 interest. They ascend the rivers in spring or early summer, 

 in the British Isles running up our southern rivers from February 

 to May and those of Scotland frorn May or June to July. They 

 not infrequently facilitate their journey by stealing a ride on 

 some large fish bound in the same direction, attaching them- 

 seh'es to the unfortunate victims with their sucker-like mouths 

 and feeding on their flesh en route \ As in the case of the Salmon, 

 the fish undergo considerable changes in colour at this time, 

 and the two sexes diflfer markedly in appearance. They make 

 their way to clear, shallow streams, where the bottom is sandy 

 and strewn with pebbles and the current fairly rapid. Here a 

 space is cleared in the bed by moving the stones a little way 

 downstream. This so-called nest is usually oval or roughly 

 circular in form, two or three feet in diameter, and slightly 

 hollowed out, with a pile of stones just below it. Often the 

 males are the first to arrive, and these commence nest-building 

 on their own account: soon, however, each male is joined by 

 a female who assists him in the operations. They move the 

 stones by attaching themselves to them with their suctorial 

 mouths, loosening them by powerful tugs and shakes, and 

 finally dragging them to the pile below the nest. In rare cases 

 a second female has been observed to assist the pair in this 

 work, and the male has subsequently mated with both 

 indiscriminately. The method of copulation is interesting, 

 and takes place in the following manner. The female hangs 

 on to a large stone by her mouth near the upper end of the 

 nest, and the male seizes her by the top of the head in the 

 same way, winding himself partly round her, the bodies of 

 the two fishes being arranged so as to form an ellipse. They 

 then vibrate the hinder parts of their bodies with great vigour, 

 stirring up the fine sand in the process, and the ova and sperms 

 are simultaneously extruded. The eggs are covered with a 

 sticky substance to which particles of sand adhere, and they 



