96 WILD LIFE OF SCOTLAND 



The former has a darker shade along the back, 

 from which he gets the name of Black Jack, and 

 the trace of a barbel under the chin ; the latter is 

 known by his protruding lower jaw. The coal-fish 

 is much the commoner form in the North Sea, the 

 lythe perhaps has the advantage on the west coast. 



Whereas the professional freebooters of the 

 deep are erratic in their movements ; depart and 

 return according to no rule, not even the abund- 

 ance of prey ; and may be absent for a long time 

 without any apparent cause ; the coal-fish is always 

 on the scene, and ready for action ; and, whereas 

 many of the sharks, and their kindred, notwith- 

 standing their bad character, are contented with 

 lowly diet, the coal-fish exacts his daily tribute 

 of highly organised victims. 



Nevertheless, there is something in the equipment, 

 and very appearance of the true predatory fishes, 

 which unmistakeably marks them off for their 

 vocation. The more or less pointed head, passing 

 into the cylindrical body, furnished with ample 

 fins, and ending in a powerful tail, give the needful 

 speed in pursuit, while the wide gullet enables them 

 to swallow large prey. 



More characteristic still is the formidable array 

 of teeth, fitted not only to grasp, but also to retain 



