COURTSHIP AND NURSERY DUTIES. 101 



during the month of June, killed by fighting. 

 The male salmon is further remarkable on account 

 of the fact that during this season of the year — 

 when he is fighting — the lower jaw becomes 

 elongated, and turns upward and backward into 

 the mouth, hook-fashion. When the mouth is 

 closed, this hook-like projection is received into 

 a special cavity in the upper jaw. The purpose 

 of this hook is not very clear, but it seems to be 

 that of stiffening the jaw to prevent dislocation, 

 which might otherwise follow one of the desperate 

 charges which they deliver, ram-fashion, upon 

 their opponent in fighting. An American species 

 of salmon develops large tusk-like teeth, which 

 inflict serious wounds. Besides this peculiar 

 hook to the jaw, the salmon also, at this time of 

 the year, becomes more brilliantly coloured. 



The little stickle-back (Gasterosteus) of our 

 streams and ditches battles fiercely with his 

 fellows for the possession of his chosen. 



By a natural sequence we pass from these 

 fierce battles or ecstatic cortortions, harlequin- 

 ades and displays, the tokens of what we may 

 call love-sickness, to a review of the more im- 

 portant facts concerning the deposition of the 

 eggs, and the often elaborate preparation for 

 their reception and safe-keeping. The range of 

 variation in the form, number and size of these 

 eggs is enormous. Much of this variation is 

 due to the fact that the egg of the fish differs 

 from what we may regard as the typical egg — 

 the hen's egg — in that it is never enveloped in 

 a hard limy shell, but, on the contrary, is gener- 

 ally quite unprotected. Such eggs are globular 



