102 ANNALS OF SCOTTISH NATURAL HISTORY 



We now turn to theories of mechanical injury. It has been 

 suggested that this abnormal condition may have been caused by the 

 fish nibbling each other's tails, and I must own that I have once, in 

 the small aquarium attached to the Museum, seen a trout, which was 

 subjected to some persecution by his neighbours, succeed in getting 

 his caudal fin nibbled into a tolerably good imitation of that of a 

 Loch-na-Maorachan trout. But it is pretty certain that simple 

 nibbling would not produce the appearance of the extremities of the 

 rays as depicted in PL V. Fig. 3, and moreover, when we consider 

 that this abnormal condition is liable to attack every fin, even to the 

 pectorals, with the one strange exception of the dorsal, the " nibbling " 

 theory must fall utterly to the ground. A pugnacious trout would 

 much more easily get at his neighbour's dorsal than his pectoral 

 fin! 



Again, it has been suggested that mechanical friction by contact 

 with or rubbing against hard rocks or stones in the bottom of the 

 lake may have something to do with the production of the Docked- 

 tailed condition. It is pointed out that Loch-na-Maorachan is shallow 

 with a rocky bottom of hard quartzite ; while Loch Enoch, though 

 very deep, has a floor or at least shore of fine hard granite sand ; 

 and there is a certain attractiveness in the idea that the delicate 

 extremities of the fins may be injured or worn by coming roughly in 

 contact with such hard rocks, stones, or sand. It is indeed not 

 inconceivable that such friction might set up an inflammatory pro- 

 cess, which might result in the arrestment of the normal development 

 of the fin-rays and the distortion of their extremities. It is remark- 

 able that besides the caudal, the affected fins are those on the under 

 surface of the body, the dorsal remaining normal. But the upper 

 lobe or half of the caudal fin is affected in the same manner as the 

 lower, so that Mr. Adam Skirving remarks in a letter to Mr. Harvie- 

 Brown, " Had it been only the lower part of the tail that was 

 defective, I should have accused the fine white sand of wearing it." 

 Moreover, one would suppose that the ventral fins were more exposed 

 to such friction than either the anal or the pectorals, and yet they are 

 comparatively rarely affected by this condition. 



It has also been suggested by some of my friends that injury to 

 the fins originally inflicted in the way referred to above might become 

 hereditary, and this, if true, would be a most startling refutation of 

 the Weismannian doctrine of the non-transmissibility of acquired 

 characters ! But I fear it has still to be proved, and that the 

 mystery of the phenomenon which has formed the subject of this 

 paper has not yet been penetrated. 



One word in conclusion. Not having seen the Gonar Burn 

 specimens, I do not know the special nature of the affection of their 

 caudal fins. The Carron specimens are not quite the same as those 

 from Islay and Galloway, and in them the malformation may be 



