MIMICKY IN THE COMMON SOLE. 



243 



S. aurantiaca, as having a " pectoral with an ovate black spot on its hinder 

 half." In S. lascaris, from the Madeiras and Mediterranean, he describes " a 

 black ocellns edged with yellow on the extremity of the lower half of the 

 pectoral." This description applies equally to his two species, S. impar and 

 S. margaritifera. 



According to Moreau and Cunningham, Giinther's S. aitrav^imca is identical 

 with S. lascaris of the Mediterranean iSea. There is another species (Solea 

 melanochira, Moreau *) found in the Mediterranean which has the upper 

 pectoral considerably developed. This fin is of an intense blue-black with a 

 whitish border. The fin is long and is borne upon a peduncle. In varying 

 degree the blackish tint of the upper pectoral seems to be characteristic of 

 the Soles proper, and is not found in the Microchires or Monocliires nor in 

 other Pleuronectidae. If the inference is correct that the preservation of the 

 pectorals in the Soles proper may be due to their employment as imitation 

 danger-signals, it might be conjectured that the hypertrophy of the pectorals 

 in Solea melanochira is traceable to a similar function, even more conspicuously 

 developed. 



In S. vulgaris the black spot always has a definite relation to the anterior 

 border of the fin, extending backwards from its edge ; in S. lascaris the spot 

 at most just touches its border with its circumference and usually does not 

 reach so far. 



In estimating the probability of these black fins of the Soles owing their 

 existence to the phenomenon of mimicry, the mimicked forms being, in this 

 instance, the Trachinidae, we have to consider : — 



(1) That the geographical distribution of Solea vulgaris and its nearest 

 allies is closely similar to, if not identical with, that of the two common species 

 of Trachinus. 



(2) That the sand-loving and sand-hiding habits of the two forms are 

 closely similar, and that they actually inhabit the same grounds, the young 

 Soles with T. vipera and the adults in deeper water with T. draco. 



(3) That on disturbance each type holds its black fin erect in a menacing 

 manner ; that of the Sole is held at right angles to the normal position for 

 Pleuronectidge. 



(4) That the pectoral fin of other Pleuronectidae, or even Soleidse, is not 

 coloured black, and is not held erect in the same manner. 



The use of black as a warning colour is significant. In land animals we 

 are familiar with black, combined with red or yellow, being employed for 

 this purpose, but the general facts of marine coloration seem to show that red 

 or yellow are, in the presence of reddish tints on sea-floor and amongst 

 seaweeds and zoophytes, colours of concealment rather than the reverse. 



* Revue et Magasin de Zoologie, 1874, t. xi. p. 115. 



