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Show 434 MR. E. w. L. H O L T - S T U D I E S I N [May 1, of the preserving fluid. The scales and sensory filaments of the under surface are perfectly normal, subject to the trifling exception just noted, and have therefore been omitted from fig. B. It may be remarked that in North-Sea Soles filaments extend on to the bases of the first few dorsal fin rays, but otherwise have the same distribution as is depicted in Cunningham's figure. The left eye is situated nearly opposite to the right eye, but is slightly dorsal to it, and about half a length further back. Belative to the mouth the two eyes occupy nearly the same position, the difference being accounted for by the greater length and dorsal displacement of the gape on the left side. But, whereas on the right side tbe whole of the iris is exposed, and the whole eye is somewhat elevated and within certain limits freely movable (either by the muscles or by the peculiar mechanism dealt with in the previous section of this paper), on the left side the eye is to a great extent embedded in the skin (see fig. B ) . Only about half the iris is visible, and even some part of the lens is obcluded, and the sensory filaments, which extend right up to the cornea on the ventral side, mast, when erect, have considerably interfered with the animal's vision. The whole eye is antero-ventrally rotated from what we may suppose to have been its original nearly lateral aspect, and I should think the fish could see but little except in the directions indicated, while the prominence of the lips must have been a further impediment to its sight. N o movement could have been possible except such as involved a general movement of the skin in this region ; but, as the skin is always loose here to allow of the expansion of the accessory visual sac, one may suppose that the eye may have been shifted to whatever extent the length of the eye-muscles permitted. The appearance it presents is that of being gradually overgrown by the skin, or of being withdrawn by some internal agency within the tissues of the head. The whole of the left surface of the fish is absolutely devoid of pigment, with the exception of a slight extension of colour below the mouth, which I have already attributed to post-mortem changes, and of certain patches of colour on the caudal fin and a small dark spot near the posterior end of the body. Such markings of the extreme posterior region of the under surface are, however, as often present as absent in normal Soles. The left eye is as bright as its fellow of the opposite side and of the same colour, and, staring out of a dead white surface, presented rather a bizarre effect in the fresh condition. The whiteness of the underside is perhaps one of the chief peculiarities of the specimen. The Cyclopean condition, comparatively common in the Flounder (PI. flesus) and, according to my own experience, commonest of all in the Turbot (Rh. maximus), is always accompanied by a more or less complete pigmentation of the blind side. In fact, as has been pointed out by Cunningham and MacMunnl , complete ambicoloration has been observed only 1 " On the Coloration of the Skins of Fishes, especially of Pleuronectidas," Phil. Trans. 1894, p. 806. |
