316 ME. F. DAT ON SOME BRITISII FISHES. 



Eyes in the normal position. The whole of the under surface 

 of the body, except the head, coloured similarly to the upper 

 surface. 



SOLEA VULGARIS. 



Length 11£ inches ; D. 76, A. 67. Eyes in the normal position. 

 The whole of the under surface of the body except the head 

 coloured as on the upper surface. 



These two specimens afford proof that the position of the 

 upper eye is not necessarily correlated to the colour which exists 

 upon, or is absent from, the under surface of the fish. In most 

 of the double examples, or those coloured on both sides, which 

 I have previously obtained, doubtless the upper eye has had its 

 progress arrested when in course of passing over to the opposite 

 side of the head — apparently confirmatory of the theory which 

 has been advanced, that the under surface becomes etiolated, due 

 to the loss of influence of the organ of vision over its pigment- 

 cells ; and that in double examples the colour is due to the eye 

 not having been completely transferred, and still retaining its 

 power. Other theories have been advanced, but it would seem 

 by no means unworthy of consideration whether these double 

 flat fishes are not retrogressions towards what existed in an 

 earlier stage of development. 



Pletjronectes flesus. 



This example, from the Westminster Aquarium, is 3 inches 

 long ; D. 61, A. 41. Eyes normal ; anterior half of body dark ; 

 posterior half white blotched with brown; caudal fin mostly 

 grey; some blotches on dorsal and anal fins; under surface -of 

 the body white. Here the eyes were normal on the usual side, 

 yet the posterior half of the body was white blotched with darker. 

 Some authors have considered these more or less albinos, or as 

 sports due to crossing. 



OSTEACION QTJADRICORNIS, Linn. 



Couch, in the ' Intellectual Observer,' v. p. 407, remarks that 

 one of these fish, residents of the tropical parts of the Atlantic 

 Ocean, had been taken in Cornwall in a net at some rather con- 

 siderable distance from land ; and in his ' Eishes of the British 

 Isles ' it is figured at pi. ccxlii., leaving no doubt as to the species 

 alluded to. 





