1894.] TELEOSTBATT MOIIPHOLOGY. 439 



ventral abdominal region is flattened, it is nevertheless rather 

 darkly pigmented, and to me it certainly seems more probable that 

 the Pleuroaectidae of the present day began to take on their 

 asymmetrical characters as compressed and uniformly coloured 

 forms than in the condition of ordinary round fish. 



A feature which appears to me to be of the highest importance 

 is the fact that ambicolorate fish appear to be always what one 

 may term "ambiciliate " also. That is to say, whenever pigment 

 is found on the blind side of a fish, the scales in that region are as 

 rough as those of the other side (in such forms as exhibit 

 asymmetry in this respect), or, at all events, are rougher than on 

 the blind side of normal examples of the same species. The Turbot, 

 for instance, which normally has no spines on the blind side, always 

 possesses them if ambicolorate. They are usually confined to the 

 pigmented region, but may occur also on the white part of the 

 skin, but only, according to my own experience, in specimens 

 which exhibit some pigmentation or other of the blind side l . 



I am not aware that it has been contended that the action of 

 light can have any effect on the development of the spines or scales, 

 and Mr. Cunningham's experiments yield no information on the 

 subject, since in his most perfectly coloured Flounders (op. cit. 

 pi. 53) practically no pigment manifested itself in the regions 

 corresponding to the site of the only tubercles which British 

 examples of Pl.flesus possess. If we admit the inefficacy of light 

 in this respect, it becomes evident that we are dealing with a 

 phenomenon in which the pigmentation is not the only element of 

 importance. The reversion, in fact, if such it is, extends to the 

 derma generally, and not merely to its power of producing the 

 various elements of coloration. 



I have shown 2 that the Turbot in its early pelagic stages is 

 possessed of a very powerful cephalic armature, and that the larvae 

 of another sinistral form, perhaps the Brill, are equally well armed, 

 though in a different manner 3 . It is possible to regard these 

 cephalic spines either as protective structures, in essential relation 

 to the pelagic period of existence, or, perhaps with greater 

 probability, as of merely ancestral significance. In a future 

 communication I hope to be able to show that the dermal spines 

 or tubercles of our British Turbot are undergoing, or have 

 undergone, a reduction in number, so that the condition of the 



1 I am speaking now of British examples only, since Turbot from the 

 Norwegian Fjords not uncommonly possess spines on the colourless blind side. 

 Norwegian Turbot, however, are much more profusely spined on the ocular 

 side than their British allies, and the spinulation of the blind side, when present, 

 is always much inferior to that of the other. I have never seen an ambicolorate 

 example from Norway ; but only a few hundred fish have come under my 

 notice, and it is possible that "double" specimens may have been withdrawn 

 by the consignors, since such are not supposed to have a high market value, 

 except for naturalists. Besides being more spinous, these Turbot appear to be 

 also considerably smaller than our own. 



2 Journ. M. B. Assoc. 1892, p. 402. 



8 Trans. E. Dubl. Soc. v. 1893, pi. xii. 



29* 



