APPENDIX. 91 



selected, they dart their snouts into the gravel, burrowing 

 with them into it ; this burrowing, assisted by the power 

 of the fins, is performed with great force, and the water's 

 current aiding, the upper part or roof of the excavation is 

 removed ; the burrowing process is continued until a first 

 nest is dug sufficiently capacious for a first deposition of 

 ova ; then the female enters this first hollowed link of the 

 bed, and deposits therein the first mature portion of her 

 ova. That done, she retires a little down stream, and the 

 male instantly takes her place, and pouring by emission a 

 certain quantity of the milt over the deposited ova im- 

 pregnates them. After this, the fish commence a second 

 excavation immediately above the first, and in a straight 

 line with it ; in excavating, they relieve each other. When 

 one of the fish gets tired of the work, it drops down 

 stream until it is refreshed, and then with renewed powers 

 resumes its labours, relieving at the same time its partner 

 who had relieved it. Their labour progresses by alternate 

 relief and exertion. The second bed completed, the 

 female enters it as at first, again depositing a portion of 

 the ova, and drops a little down stream ; the male forth- 

 with enters the excavation and impregnates the ova in it. 

 The ova in the first part of the bed is covered by the 

 sand and gravel dug from the second part being chiefly 

 carried into it by the action of the current. The excava- 

 ting process just described is continued until the female 

 has no more ova to deposit. The last deposition of ova 

 and milt is covered in by the action of the fish and 

 water, and breaking down of some of the gravel bank 

 above and over the nest. Thus is formed a complete 

 spawning bed, not at once, not by a single effort, but 

 piecemeal and at several intervals of greater or less dura- 

 tion, according to the age and size of the fish, and quan- 

 tity of ova and milt to be deposited. A female salmon in 

 its third year has a larger quantity of ova than a female 

 grilse or young salmon in its second year ; and it may be 

 taken for granted that the older and larger the fish, male 

 or female, the greater is the quantity of ova to be depo- 

 sited and milt to be emitted. In consequence, the time 

 occupied in deposition depends upon the size and fecun- 

 dity of the female fish. The average time is from five 



