434 



THE DESCENT OF MAN 



during the breeding season, besides a slight change in color, 

 "the lower jaw elongates, and a cartilaginous projection 

 turns upward from the point, which, when the jaws are 

 closed, occupies a deep cavity between the intermaxillary 



Fio. 27.— Head of male common salmon {Salmo solar) during the breeding season. 



[This drawing, as well as ail the others in the present chapter, have been executed 

 by the well-known artist, Mr. Q. Ford, from specimens in the British Museum, under 

 the kind superintendence of Dr. Guntner.] 



bones of the upper jaw" ' (Figs. 27 and 28). In our salmon 

 this change of structure lasts only during the breeding 

 season; but in the Salmo lycaodon of N.-W. America the 



' Yarrell, "History of British Fishes," vol. ii., 1836, p. 10. 



