100 CARTILAGINOUS PROJECTION. . 



also cause hindrance to the free flow of water to the lungs, 

 were it not for a web, forming a sort of hanging ceiling, 

 attached in front and at the sides to the jaw, but open in 

 a parabolic form behind. This vault is so large in a twenty- 

 pound fish, that between it and the hanging ceiling the 

 finger may be inserted from behind, nearly up to the second 

 joint. 



After the termination of the spawning season the protube- 

 rances on both jaws are gradually absorbed, and the head of 

 the fish resumes its ordinary shape. 



On the first appearance of the male salmon in the Save in 

 spring, he is entirely without the excrescence spoken of, or at 

 all events has only the very germs of it ; and throughout the 

 summer its growth is slow, but it increases more rapidly 

 towards the spawning season, at which period it has attained 

 its full development. 



No elongation whatever takes place on the jaws of the 

 female salmon. They remain in the same state all the year 

 round. 



It is the commonly received notion that the hook on the 

 lower jaw of the male salmon is for the purpose of enabling 

 him to assist the female in forming a hole in the bed 

 of the river, for the deposit of her roe. But such Mr. 

 Keiller convinced himself is not the object for which it is 

 designed. In his opinion, it is intended to prevent the 

 males, which in the spawning season are most pugnacious, 

 from killing each other ; for when the jaws of even a 

 twenty-five-pound fish are distended to the utmost, the hook 

 is so much in the way that the opening in front of the 

 mouth will admit little more than the breadth of a finger, 

 and consequently he cannot grasp the body of an anta- 



