RAPPORTS. XIII C4: MASTERMAN 



20 — 



Table 1. — The vitality of male fish relative to that of female fish'of the same size. 



Size of Fish (cm.) 



12—13 



14—15 



16—17 



18-19 



22 — 23 



24—25 



26—27 



Average 



Number of Fish treated 



Number of comparisons 

 made 



Probable error of diffe- 

 rence of averages. . . . 



o-8s 

 651 



I'29 



I2I4 



ro8 

 1094 



31 



973 

 35 



f29 



775 

 31 



'•IS 



727 



27 



i-i8 

 3S9 



16 



o'gG 

 64 



o"o6 



0.06 



o'o6 



o-os 



0.05 



cog 



Somewhat more interesting is the comparison of the vitality of plaice of the same 

 sex but of different size. 



Both sexes were found to increase in power to resist injury with increasing size: but 

 whereas the rate of increase was continuous in the case of the females, it gradually declined 

 in the males. Unfortunately the plaice of over 30 cm. in length were insufficient in num- 

 ber to permit of investigation: it is however probable that the decline in the rate of in- 

 crease in the males is connected with the approach of maturity, and the consequent 

 diversion of the resources of the body from somatic to reproductive ends. In this case 

 experiments with larger females should show a similar decline in the rate of increase of 

 vigour as the size of their first maturity is approached: but it is not impossible that the 

 differences shown between the sexes may even point to difference of stamina, or earlier 

 exhaustion in the males, constituting one of the factors which result in the great scarcity 

 of the larger or older males in the North Sea which has been noted by W.'vLLace. 



The following table shows the rates of increase of each sex with size. The constancy 

 in the case of the females and the decline in the case of the males is marked. 



Table 2. — Vitality relative to a group of smaller fish. The fraction representing the vitality 

 at each size-group has been divided by that representing the vitality of a group 6 cm. smaller 



but of the same sex. 



Size (cm.) 



Male 



18 — 19 20 — 21 22—23 24 — 25 26—27 



12-13 



14-15 



16 — 17 18—19 



Female 



18—19 



12—13 



20—21 23 — 23 



-15 



16—17 



24-25 



18-1S 



26 — 27 



19—20 



Average 



Number of fish treated . . 



Number of comparisons 

 made 



Probable error of difference 

 of average 



I -89 

 616 



'S 



I '93 

 648 



17 



i'8i 

 456 



18 



i'34 

 222 



i'o7 

 100 



0'24 



0"24 



o'og 



1-65 



14 



1-65 

 825 



1.69 

 624 



23 



1-63 

 450 



iS 



1-71 

 335 



16 



o'i5 o'i5 o'li 



