168 



MKRISTir VARIATION'. 



[PART i. 



(Such a development of tuln-rcles 1 on the lower side may however occur 

 without any con-flati-d rliange of colour.) It is also stated that in 

 tin- "douhle" turl.nts tin- muscles of the lower side are thicker than 

 tln-y normally a iv, thus approximating to the upper side, a feature 

 that may be taken as an indication that the manner of swimming is 

 dillerent from that of normals. 



A tlat-tish having pigmentation on the lower side does not 

 necessarily j>iv>ent any other abnormality 2 . The Plaice, for in- 

 stance, just mentioned, was, colour apart, quite normal. But 

 some specimen^ of Hat-fishes darkly coloured below present in 

 addition a very singular structural variation. This consists essen- 

 tially in the presence of a notch of greater or less depth occurring 

 belcro tin anterior end of the dorsal tin above theeye (Fig. 152). By 

 I his cleft the anterior end of the dorsal fin is separated from the 

 l>aek of the head and is borne on a process or horn project- 

 in - anteriorly so as to continue the contour of the body above the 



FICJ. 152. Head of a Brill (lUm/nlni* he via) having the dorsal fin separated from 

 the head as described in the text. (From YAIUUXL.) 



1 The literature relating to discontinuous variations consisting in the presence 

 of bony tubercles upon the blind side of Khombi is extensive. See especially 



' 



DEMIDOFF, Voy. dan* In Huxxif Mi'rid., 1840, in. p. 534, Pis. 28, 29 and 30. 

 STEINDACHNER, Sitzb. Ah. H7.->. !!'/,, 1868, LVII. (1), p. 714. EATHKE, Mem. Ac. 

 Sci. 1','t., 1837, in. p. 349. GPNTHEB, Cat. llrit. Mit.<. l<'ix)i,>x, iv. p. 409. These 

 - will not be confounded with those of supposed hybrids between R. ma.rimus 

 and /,'. /<///>, which hear upon both sides scales of various sizes. 



- I know no detailed description of a flat-fish wholly pigmented on the underside, 

 having the dorsal fin normal, but numerous authors (Gottsche, Duhamel, &c.) make 

 mention of such cases. Since this chapter was written 1 have seen two recent papers 

 on the subject by GIARD (Comptt-s reml. Si><\ 1:/<>I. , Is;i2, S. ( .t, iv. p. 31 and Nut. ,SV/., 

 IS'.IH, p. 356) contributing furtla-r ovideuce on the subject and giving new cases in 

 the Turbot. According to (liard, of tlounders (/'. //<.-(/.-) at Wimeruux 3 / are fully 

 coloured on the blind side, in addition to many that are piebald. This must be a 

 very much higher proportion of abnormal specimens than is found in English 

 fisheries. 



