The Natural History of the Salmon. 5 7 



entire head longer than the females ; with the 

 intermaxillary bone the teeth, with which it is armed, 

 are also enlarged, sometimes to four times the size 

 of those of the females. And if this development of 

 the front part of the head happens to be going on 

 while the individual is able to obtain only a scanty 

 supply of food, the usual proportions of the head 

 and trunk are so altered that the species is very 

 difficult to recognize. Barren male fish approach 

 the females in the proportions of the head and 

 body, but hybrid fishes do not differ in this respect 

 from their parents. The abundance or scarcity of 

 food, and the disposition or indisposition of the 

 Salmonoids to feed, are other causes affecting the 

 growth or fulness of the various parts of the body. 

 In well-fed fishes the head is proportionally not 

 only smaller, but also shorter, and vice versA. 



" The^foj vary to a certain degree. The variation 

 in the number of rays is inconsiderable, and of no 

 value for specific distinction. The caudal fin under- 

 goes considerable changes of form with age, and 

 dependently on the sexual development. Young 

 specimens of all species have this fin more or less 

 deeply excised, so that the young of a species which 

 has the caudal emarginate throughout life, is dis- 

 tinguished by a deeper incision of the fin, from the 

 young of a species which has it truncate in the adult 

 state. As the individuals of a species do not all 



