of the Fishery Board for Scotland. 



233 



Dr. Petersen's specimens may have been measured when alive, and 

 unequal contraction may account for the approximation of these sizes; 

 but the conclusions from these measurements are that for the pelagic 

 stages, free-swimming, the pupil of the eye is of the same size for both, 

 the difference being so slight as to come within the possibilities of errors 

 in measurements, and that, when the plaice takes to the shallow waters 

 at the tidal margin, and the dab sinks to the bottom in deeper waters, 

 the pupil of the dab increases in size faster than does that of the plaice. 



A note was also made of the number of fin-rays, though at these early 

 stages, when the bones are not hardened, the fin-rays are most subject to 

 injury. For this reason only a few, in comparison with the large 

 number that had to be disregarded, could be counted. The numbers are 

 contrasted with those given by Day"^ and Petersenf. 



For Dab, D. 70 to 77. Day, D. 65 to 78. Petersen, D. 65 to 73. 



A. 50 to 61. „ A. 50 to 62. „ A. 51 to 55. 



For Plaice, D. 68 to 77. „ 66 to 77. „ 61 to 80. 



A. 50 to 56. 50 to 57. 46 to 57. 



For Flounder, D. 58 to 64. „ 60 to 62. „ 49 to 65. 



A. 38 to 46. „ 39.to.45. 33 to 43. 



The point worthy of note is the great variation of the flounder and 

 plaice recorded by Dr. Petersen. D. 60 to 62 for the flounder, given by 

 Day, does not represent the variation in the number of dorsal fin-rays. 



Mr. Cunningham! has recently given a large enumeration of the 

 variations in characters of plaice from diff'erent regions. The variation 

 in fin-rays is D. 67 to 81, A. 49 to 60. The higher numbers occur more 

 frequently in the females, and more frequently in those from the south 

 of England than in those from the east, but the difference is slight. 



The question of the distribution of pigment is the most difficult to 

 deal with, especially' from spirit specimens. Mr. Holt says that " a 

 general pigmentation of the ocular side is assumed by the young plaice at 

 a smaller size than in the case of the dab." Since metamorphosis is 

 complete in the plaice earlier than in the dab, and the young plaice sink 

 earlier to the bottom, this general pigmentation is the consequence. 

 During the pelagic stages the distribution of pigment on the plaice and 

 the dab is the same for the most part — a varying number of groups along 

 the interspinous regions and on the fin-rays, along the lateral line, and 

 detached spots over the rest of the body and on the head. This seems to 

 be the maximum of pigment, and varies considerably. It is present on 

 both sides, though fainter on the left, during the transformation stages. 

 It seems, therefore, to have its origin during the symmetrical and early 

 transformation stages. 



When the pelagic stage is prolonged, as in the dab, long rough dab, and 

 lemon dab, black pigment appears along the lines of the myomeres. Its 

 presence is very variable, however. If pigmentation depend upon one 

 chemical compound, and the various colours are simply the result of the 

 presence of this compound in varying quantities — the smaller quantities 

 giving rise to red or yellow, etc., a large quantity giving rise to black — it 

 €an be understood why black is more permanent than the others, and why 

 what is coloured red or orange in one form is black in another. In living 

 specimens of the early transformation and symmetrical staj^es one would 

 expect to see coloured pigmentation on fin-rays and interspinous regions 

 where afterwards the iDlack appears. While the pigmentation of the 

 plaice and the dab is the same during the pelagic stages, the increase of 

 pigment in the plaice at an earlier stage is a secondary effect, due to 



* Day, British Fishes. 



t Loc. cit., p. 128. 



X J. M. B. A., March, 1897. 



