10 



Immature Females. 



Owing to the labour involved, collective results for all tlie fish in each quadrant, 

 male and female, adult and immature, were calculated only for one experiment, 

 viz. No. 9. The total number of plaice recaptured, about which the necessary 

 particulars were obtained, was 120. The results were as follows : — 



71, or 59'1 per cent., migrated in the mean direction N. 28° E., the aggregate miles 



being 5207-6, and the average 73"3. 

 28, or 23*3 per cent., migrated in the mean direction N. 63° W., the aggregate 



miles being 491-6, and the average 17*6. 

 7, or 5"8 per cent., migrated in the mean direction S. 29° E., the aggregate miles 



being 456-4, and the average 65*2. 

 14, or 11*6 per cent., migrated in the mean direction S. 68° W., the aggregate miles 



being 151*3, and the average 10'8. 



III. A third method was adopted for the experiments at 20 miles east of the 

 Isle of May, by calculating the resultant not for each of the quadrants separately 

 but for all directions together, so that the net result of the migrations of all the 

 recaptured plaice might be represented by a single line. These calculations were 

 kindly made by Dr. Tocher, Lecturer on Statistics, University of Aberdeen. In 

 this case also, the sexes were considered separately, adults being distinguished from 

 immatures, and the direction taken by each fish throughout the whole of its migra- 

 tion was taken into account, and not merely, as in the above methods, the initial 

 direction of those which went northwards and then passed westwards. The 

 distinction affects only those which turned westwards into the Moray Firth, or 

 farther, and not those found to the south of the Moray Firth. For example, one 

 of the marked plaice from Experiment No. 5 was taken south of Cape Wrath, and 

 the directions and distance drawn on the chart from the station where it was 

 liberated to the place at which it was recaptured are as follows : — N. 24° E. 85 miles ; 



