240 DR. A. T. MASTERMAN ON A POSSIBLE CASE OF 



the fish and with the hght drab of the sand, makes it clearly visible from a 

 considerable distance. It has been suggested by Garstang that this is a case 

 of warning coloration. Considering the poisonous nature of the fish and its 

 abundance, one cannot doubt that this black danger signal must act as 

 a powerful deterrent to its enemies *. If this is the case, the habit of 

 ago-regation into large shoals would be beneficial through accumulative 

 warning action. 



The right or upper pectoral fin of the Common Sole (Solea vulgaris) is 

 well developed, and the upper half of the fin has a large, deep black patch. 

 This patch is, as remarked by Smitt, more conspicuous in the young Sole than 

 in the adult, but it is a clearly recognizable feature throughout life, except in 

 the very earliest stages. When a number of Soles are displayed in the 

 market, the little black dot in the pectoral region of each fish can be seen at 

 some considerable distance. 



The habitat of the Sole is well-known. " The usual depth at which Soles 

 are found is from 20 to 30 fathoms, but it may exist at greater depths ; it 

 probably does not extend beyond 100 fathoms. ' Adult Soles may occur at 

 any depth less than 20 fathoms ; but usually in shallow water, less than 

 10 fathoms deep, only young individuals are found " f. 



Cunningham goes on to describe the habit of the Sole of burying itself in 

 the sand and instinctively going through the motion of doing so when placed 

 upon the bare floor of a tank. " Usually when resting undisturbed beneath 

 the sand or gravel it leaves its eyes uncovered, and these can be detected by 

 careful search," 



The smaller fry of Soles, like the Lesser Weever, are commonly found on 

 the shallow sandy fiats worked by shrimp-trawls. 



The Sole therefore resembles the Weevers in the soft or sandy nature of 

 the ground frequented by it, in the depth of water, and in the habit of con- 

 cealing itself under the sand. 



The general distribution of the Sole is well-known. It occurs in small 

 numbers off the coasts of Norway, and only ranges to 62° N. (Collett). It 

 is scarce in the Baltic, though found in more abundance in the Skager-Rak 

 and the Skaw. In the southern half of the North Sea, as represented by a 

 line from Flamborough Head to the Naze, it is common, but is found in 

 greatest abundance in the English and Bristol Channels. It ranges south- 

 wards along the Atlantic seaboard of Morocco and into the Mediterranean. 

 It is found off the coast of Scotland, but is not a common fish north of 

 Berwick. 



The suggestion here made is that the black patch of the pectoral fin in the 

 Sole is a case of mimicry in relation to the black dorsal fin of the Weever. 



* Poulton, ' Colours of Animals,' p. 164 ; Camb. Nat. History : Fishes, &c. p. 174. 

 t ' The Sole,' Cunningham, p. 101. 



