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Show 436 MR. E. W. L. HOLT-STUDIES IN [May 1, of the dorsal is free. Besides the specimens in question, I have seen similarly malformed Turbot on several occasions in the Grimsby market, and have no doubt but that the malformation is common enough. As the authors remark, this condition differs from the Cyclopean only in degree, and I would suggest that the explanation offered above as to the process of development of the Cyclopean malformation is equally applicable to that now under consideration, allowing, of course, for a less degree of want of harmony in the metamorphosis. But, again, quoting Messrs. Cunningham and MacMunn, " it is a very great difference of degree, and does not contradict the conclusions . . . . formulated as to the correlation of the typical malformation with ambi-coloration." That is true enough, but since the partial malformation is not necessarily accompanied by ambicoloration, it would seem possible to restrict the correlation to the abnormality of the eyes. The Brill, as described by the authors, is colourless on the blind side, except for a small patch of pigment just behind the notch of the dorsal, and continuous, through the notch, with the pigment of the ocular side. The inner face of the notch is rounded, there being no abrupt line of demarcation between the ocular and blind sides ; and I a m inclined to regard the intrusion of colour as due simply to a migration of chromatophores. Pigment commonly extends on to the blind side of the ventral part of the head in PI. microcephalia, the ventral edge being in this form rounded instead of somewhat abrupt. I have also a young Plaice (PI. pla-tessa) which has in some manner been cut through down to the backbone. The wound has healed without the anterior and posterior regions re-uniting, and a certain amount of pigment extends through to the blind side. I think it may therefore be assumed that the Brill is practically normal in the coloration of the blind side. The Turbot has a good deal of pigment on the posterior region of the blind side, but others, with a similar hook of the dorsal, I have noticed to be entirely colourless on the blind side, and pigment, as noticed by the authors referred to and others, occurs so commonly, and sometimes to so considerable an extent, on the blind side of otherwise perfectly normal Turbot that there is no reason to suppose that the malformation of the dorsal in this particular specimen has any necessary connection with its partial ambicoloration. The authors mention the frequent occurrence of Turbot and Brill with a row of spots along the interneural and interhaemal regions of the blind side, and certainly, in the North Sea, Brill so marked are extremely plentiful. I have not observed it so commonly in Turbot, the reason being, as I supposed, that such spots are usually marked by a more or less diffuse arrangement of the pigment in ambicolorate Turbot. I do not find any suggestion that these markings of the blind side of the Brill are precisely those which are the most conspicuous in the metamorphosing and |
