SALMON— SEXUAL DISTINCTIONS. 57 



If early ascent is interent in a race, it must be evident that were the eggs of 

 such transferred to a " late " river, it would cause the introduction of an early- 

 ascending breed of salmon.* 



Sexual distinctions. — The male at the breeding season has a hook, knob, or 

 kype developed at the upper surface of the end of the lower jaw, which dis- 

 appears by degrees, often by the time it has become a well-mended kelt, unless 

 the fish is a very old one,t when the bony portion of this swelling cannot be 

 absorbed. (Plate 1.) The cause of the existence of a knob on the lower jaw 

 of male salmon and trout has been a fruitful cause of discussion from ea.rly ages 

 down to the present day. We find that male pars or smolts whose milt is capable 

 of fertilizing eggs possess no such knob, but as years pass, one becomes more and 

 niore prominent. It annually augments at the breeding season and partially 

 diminishes in size subsequently, as age advances that portion of the head which 

 is anterior to the nasal valves seems to double its previous proportional length 

 or what is seen in the female. At first the lower jaw increases in length more 

 than do the bones of the snout ; consequently, the prenasal portion is found to 

 be only one-half of the comparative length to what obtains in very old fish, 

 but as the knob growg on the upper edge of the extremity of the mandibles, it is 

 placed when the mouth is closed anterior to the front edge of the snout, where 

 there is often a sore spot caused by abrasion. But after a few years the snout 

 and upper jaw commence growing more rapidly than the mandibles, and as a 

 result, the knob becomes overlapped by the snout, and then it presses against 

 and is received into a large depression, situated between the two ascending 

 portions of the premaxillaries which are freely movable. Thus, although the hook 

 may press against the palate, it can do so without occasioning any injury, because 

 the parts give way before it. But should any irritation occur at this spot it might 

 ulcerate through the soft parts, when it would appear above the snout or on the 

 upper profile of the head. When this takes place, movement in the upper jaw 

 would be difficult or impossible, and the fish would as a consequence become 

 starved. 



The knob appears to be entirely composed of connective tissue, J so cannot fall 

 ofE, but may be more or less absorbed, § as it doubtless is after the breeding season. 



is of others : to the temperature of the water or to the unwholesomeness of some rivers, either 

 acting directly on the contained fish, or in a secondary degree through the medium of their 

 offspring which may be a weaWy race. It may also be worth inquiring whether the present 

 continuous modes of fishing estuaries and capturing all the large salmon which are ascending, 

 leaving the smaller fish mostly to continue their kind, may not be causing deterioration of 



* Some rivers may possess an early and a late breed {i.e., if fish always return to the stream 

 of their birth) should it have tributary streams in which these fish can breed early or late, still 

 all must ascend the main channel. 



t July 31st, 1886, a large salmon, in fair condition, was in a fishmonger's shop at Cheltenham 

 having a very large hook, but no orange colouring, here the knob was probably persistent from 

 age : the succeeding month (August 24th) there were three more, but aU had orange markings on 

 the head and body. On June 6th, 1886, a fine 36 lb. fish had only a small and soft knob, either 

 increasing or diminishing. 



{ Professor Gadow, who was so good as to make sections of one and stain it with carmine, 

 thus remarked, " The hooks consist entirely of fibrous ooimective tissue, without any traces of 

 cartilaginous cells in it, the whole being surrounded by the epiderm. Therefore the hook cannot 

 be looked upon either as an outgrowth of the bones of the lower jaw, or as a sort of horny excres- 

 cence like horns, nails, or pads such as toads possess on the palms of their hands. But as a 

 periodical outgrowth of the cutaneous connective tissue which surrounds the body, being situated 

 between the epidermand the bone, without, however, having any relation to the periosteum. This 

 cutaneous connective tissue nature explains why and how the hook can again be absorbed, or 

 rather re-absorbed after the season is over. Certainly it cannot be shed." 



§ Several authors speak of this knob "falling off "subsequent to the breeding season, but it 

 can only be gradually absorbed, and when the bone itself grows (as seen in plate 1, fig. 1) the 

 bony tissue cannot be removed. The statement made in The Field by Mr. George, February 16th, 

 1884, must evidently have been written under some extraordinary error : "When the fish has 

 reached a certain stage in the kelt state, the hook gradually loosens at what seems on examination 

 to be a kind of joint just where the point of the nose should be in the fish, a slight tap when it 

 has arrived at this stage, or slight pressure on the gravel, will dislodge it. I have dislodged many. 



