Gattij ^Ja^^c Ldhoralori/, St. Amhcios. 20:5 



tlie eye beyond its niiddU', both sides of the body were uiii- 

 Ibrnily coloured. The fish was to all appearance normal in 

 its characters, yet no bleaching ot" the left or ventral side had 

 occurred. 



Such an exani])le raises doubts as to whether it is the effect 

 ot light or its absence which alone is responsible for the con- 

 dition in the Pleuronectids. This is further supi)orted by the 

 fact that in metamorphosing young examples the side which 

 is to be pale becomes considerably less pigmented before the 

 fishes swim obliquely or leave their pelagic life. Even when 

 the pelagic stage is greatly prolonged, as, for instance, in the 

 young turbot, by an arrest of the right eye in its progress 

 to the left, so that each side has an eye in a fish about an 

 inch in length, the same feature is noticed. Thus, in the 

 ' Invertebrates and Fishes of St. Andrews' *, fig. 5 (pi. vi.) 

 represents the right side of such a specimen, which has 

 on the whole less pigment than the left side, viz. fig. 6. This 

 feature has often been observed in smaller forms of various 

 Pleuronectids. 



Besides, the mere fact that the lateral line in such examples 

 as the dab above mentioned remains unchanged indicates a 

 condition more dee[)ly seated than so simple a cause as the 

 absence or presence of light. This will be again referred to. 

 A dab about 9 inches in length had the dorsal surface 

 normal, but the ])OSterior half of the left (lower) surface was 

 pigmeiited like the dorsum throughout. No structural abnor- 

 mality was present. 



Messrs. Cunningham and Macmunnf met with no examples 

 resembling tliis and the preceding in turbot, brill, flounder, or 

 plaice — that is, a normal outline with pigment on the lower 

 or ventral side. 



Various abnormally coloured plaice have recently been 

 procured at St. Andrews both by hook and net. 



1. In an example procured 1st February, 1901, measuring 

 about lOJ inches in length, the dorsal surface had an area of 

 about 3 inches from the tip of the snout backward of the 

 normal colour. The colour-line included half an inch of the 

 anterior border of the anal fin, and trended with a slight con- 

 vexity backward and then a slope forward to the dorsal edge. 

 The dorsal line of the coloured region was 2^ inches, the 

 ventral about 4:. The rest of the dorsal (right) surface was 

 pure white, with the exception of a small isolated patch about 

 the size of a large pea less than half an inch from an incurva- 

 tion of the dorsal edge of the coloured region. Two small 



* 1875. 



t Philos. Traus. 1893, B, vol. 184, p. 806. 



