MIMICKY IN THE COMMON SOLE. 241 



With the above facts already known, I have attempted to obtain further 

 evidence, confirmatory or otherwise, of this theory, by observation of the 

 habits of the Sole. The process of burying is effected in the case of the Sole 

 by an undulating motion of the dorsal and anal fins. Each fin is thrust 

 outwards and downwards into the sand, some of which is at the same time 

 thrown on to the back of the fish. 



In the Lesser Weever, the body of the fish works its way down into the 

 sand by side-to-side undulations of the hinder half of the body, and especially 

 the caudal fin. The pectoral fins also largely assist by a process of scooping into 

 the soft sand. In both Sole and Weever the process is very rapidly and 

 effectively carried through, and in both the motions are performed even if no 

 sand be present. 



On the approach of an enemy it is the usual habit of the Plaice, the 

 Turbot, the Sole, and some other flat-fish to lie concealed on or in the sand or 

 loose gravel. This is persisted in until the psychological moment when the 

 fish is apparently convinced that its presence is known to the enemy and 

 that further concealment is useless. The property of the skin of flat-fish to 

 modify its coloration in accordance with the conditions of light assists 

 immensely the power of concealment ; and it is farther helped in varying 

 degree by a persistent capacity for remaining motionless which, when highly 

 developed, becomes a habit of simulating death. So far as one can judge by 

 specimens which have been for some years in the aquarium tanks, I find that 

 the Turbot and the Plaice " bolt " first, the Sole next, and the Sand-Sole 

 {S. lascaris) appears to carry the habit of quiescent lying in the sand to the 

 extreme of actually simulating death. 



But whenever the fish is aroused and seeks refuge in flight, there is a 

 marked difference in the behaviour of these species. In the Turbot and the 

 Plaice, there is a general scurry in which the pectoral fins are seen to take 

 part by quick striking movements, no doubt assisting to raise or depress the 

 head. In the Sole, on the contrary, the upper pectoral fin is erected sharply 

 and spread, either just before " bolting " or immediately thereafter, and, as a 

 rule, it is not employed as a motor-fin. It forms a motionless black flag held 

 up conspicuously like that of the Weever, and with exactly the same menacing 

 attitude. There are at the Plymouth Laboratory several large Soles which 

 have been five years in the tanks, and it is remarkable to observe how, when 

 they have been disturbed, they sail around with the little pectoral fin held 

 stiftly erect. Further than this, the fin is held up with its plane lying in the 

 central plane of the fish, though the natural position is perpendicular to this 

 plane. It is difficult to account for this very marked and persistent habit in 

 any other way than as a case of mimicry. 



The Dab (P. limanda) and, to some extent, the Flounder {P.fiesus) have 

 also a habit of holding their upper pectoral fins erect. In the former the 



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