1894.] XELE08TEAK KOBPH.OLOUV. 437 



pelagic stage, yet such, in fact, is the case. In almost all flat- 

 fish there is a tendency, even before the yolk is absorbed, towards 

 an arrangement of the pigment into several series of patches, 

 transverse to the long axis of the body. Each series consists 

 mainly of a group of chromatophores on the dorso-lateral and 

 ventro-lateral regions of the trunk, and is completed by corre- 

 sponding groups on the dorsal and ventral parts of the marginal fin \ 

 The pigment is, of course, equally developed on either side, and, as 

 the body of the larva increases in depth and the basal ridges of the 

 median fins appear, the chief colour-patches extend on to these, 

 and ultimately come to be confined almost entirely to these areas. 

 Between the primary patches of each ridge, secondary markings 

 commonly make their appearance and shortly become little inferior 

 to the original. The process is illustrated, incidentally, in the 

 drawings of almost every author who has studied the development 

 of flat-fish. The Brill, so far as I am acquainted with its 

 ontogeny, exhibits these spots as conspicuously as any metamor- 

 phosing larva, and more so than the Turbot, in which the early 

 development of a diffuse body-pigment tends to mask them some- 

 what. Nevertheless they are easily visible in the later pelagic- 

 stages of that form, and can be made out, even on the blind side, in 

 a specimen the eye of which has arrived at the ridge of the head, 

 and in which, of course, the pigment of the blind side is consider- 

 ably less abundant than that of the coloured side. On the ocular 

 side of a Brill at a similar stage of cephalic metamorphosis they 

 are shown clearly enough by Cunningham in his ' Treatise on the 

 Common Sole' (pi. xv. fig. 5). 



In later life in both the species mentioned, as also in most other 

 flat-fishes, the dark spots cease to be conspicuous, the lighter 

 intervening areas being the only markings which attract attention 

 in half-grown and adult fishes (on this part of the body). In the 

 Topknots, however, the markings remain visible throughout life 

 in Bh. punctatus and Phr. unimaculatus, while in full-grown 

 Bh. norvegicus they are as conspicuous as in the younger stages of 

 any Pleuronectid. 



The Brill of which we have been speaking less commonly exhibit 

 another marking on the blind side, in addition to the rows of spots 

 on the in terspinous ridges. This is situated on the lateral line rather 

 behind the middle of the body. A mark is very usually present in 

 this position in metamorphosing flat-fish of other species, and in 

 the Brill it persists as a rather large roundish black spot on the 

 ocular side in half-grown and perhaps also in full-grown fishes, 

 though I have not myself observed it in the latter. It corresponds in 

 position to the ocellus of Ph. unimaculatus, to the posterior spot of 

 Bh. punctatus, and to a similar marking in Bh. norvegicus. 



1 Such an arrangement of the larval pigment is by no means confined to the 

 Pleuronectida?, and any deductions that may be drawn as to the ancestral 

 significance of such pigmentation may probably be capable of a wider interpre- 

 tation than that which, for the purposes of the present paper, I have thought 

 necessary to suggest for them. 



Paoc. Zool. Soc— 1894, No. XXIX. 29 



