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Rh Salmo lycaodon of N.-W. America the change, as Mr. J. K. Lord believes, is permanent, and best marked in the older males which have previously ascended the rivers. In these old males the jaw becomes developed into an immense hook-like projection, and

Fig. 27. Head of male common salmon (Salmo salar) during the breeding-season.

[This drawing, as well as all the others in the present chapter, have been executed by the well-known artist, Mr. G. Ford, from specimens in the British Museum, under the kind superintendence of Dr. Günther.]

the teeth grow into regular fangs, often more than half an inch in length. With the European salmon, according to Mr. Lloyd, the temporary hook-like structure serves to strengthen and