z.^ KI.Al I'ISHl'S (IIICI HROSOMATA) 



In tlic Inst tyiH' thf ik'sckipnu'nt of i liroin.itoplicires in Cfitain regions of tlie slim 

 of tlie lilinil side prodnces irrcgnlar patches of dull pigment which give the lower 

 surface a stained appearance. As a rule, this coloration of the blind side is 

 considerably less marked than that of the ocular side, and lacks the characteristic 

 spots and markings of the latter. Flounders with large irregular areas, or even with 

 tile greater part of the blind side stained with brownish or grey, are quite common, 

 and a similar condition is found in Plaice, Uab, Lemon Sole and other species. It 

 seems probable that the pigmentation of tlie blind side artificially produced by 

 Cunningham in h'lounders which had been exposed for a prolonged period to the action 

 of light reflected from below the fish was of this type (Cunningham and McMunn, 

 18(34). i'"" ambicoloration described by Hussakof (1914) in two specimens of the 

 .Vmerican I'aralichthys dentatus may also be of this nature. As far as this type of 

 pigmentation is concerned, Cunningham's e.xplanation of its causation may be the 

 I orrect one. .According to his view, the pigmentation of certain regions of the blind 

 side in some Flatfishes is due to the action of light entering horizontally or obliquely, 

 and reaching areas of the skin which are not in contact with the bottom, in cour.se of 

 time causing the.se areas to become pigmented. He suggested that such a phenomenon 

 is more likely to occur among Flatfishes living on a hard ground instead of on a sandy 

 bottom, where they are unable to bury themselves in the normal manner. 



In the second type the blind side exhibits a varying number of black or brown 

 spots. Frequently these have an irregular arrangement, and present the piebald 

 appearance already de.scribed as occurring on the ocular side. I'laice and Flounders 

 with a spotted lower surface are of fairly frequent occurrence, and Bumpus (1898) 

 has described a similar condition in the American species, Pseudopleuronectes ameri- 

 lanus. Sometimes the spots and blotches have a regular arrangement, and Turbot 

 and Brill with a series of large, round, dark spots along the upper and lower edges 

 ol the body on the blind side, with or without an additional black blotch on the lateral 

 line, the remainder of the skin being unpigmented, are c^uite common. According to 

 Giard, the piebald condition of tlie lower surface is so common that it was considered 

 by Dauberton, Bonnaterre, Lacepede and other early French ichthyologists to be a 

 specific character of the Turbot. It is of some interest to note tliat these spots and 

 blotches, when present on the blind .side, occupy the same positions as the charac- 

 teristic dark spots jiresent on the ocular side in so many Flatfishes, which have been 

 shown to have been derived from ancestral vertical bars (see p. 22). They are, in 

 fact, as Holt (i8((4) has pointed out, " precisely those which are the most conspicuous 

 in the metamorphosing and pelagic stage ". 



The third type, the true ambicoloration, appears to lie of a different nature from 

 both those already described, and has an important bearing on the cjuestion of asym- 

 metry. Here the coloration of the blind side clo.sely resembles that of the ocular 

 surface, even to the characteristic spots and markings. In ambicolorate Plaice, 

 for example, there .seems to be a more or less close correspondence m position between 

 the orange .spots of the " upper " and those of the " fower " side.' True ambicolora- 

 tion is frequently partial in character, the hinder part of the blind side being coloured 

 like the upper surface, the front part remaining white. In other examples the pi,gment 

 on the bhnd side extends forward nearly to the head, and an area in the region of the 

 viscera is also coloured. In others, again, the pigmentation of the blind side covers 

 the whole body as well as a part of the head, only a patch on the anterior ]jart of the 

 head remaining white (Fig. 17). Very occasionally the ambicoloration is complete, 

 and no trace of white is to be seen on the blind side of the fish. 



Ambicolorate examples have been recorded in a number of Flatfishes (Turbot. 

 Brill, Dab, Flounder. Lemon Sole, Plaice, Sole, etc.), but the condition seems to be 

 much more common in some species than in others, and to present a more complete 

 appearance in certain forms Thus. Turbot in which the ambicoloration is complete 

 except for a patch on the head ,ire l>y no means uncommon, whereas, partially ambi- 

 colorate examples are rare. Brill (a closely related species) exhibiting any degree 



' Sn- li,,lrs..i, (iS,,,. p. ,1.;, ; l-:lTiihirst ( . f, II . p. 771. 



