GASTEROSTEUS ACULEATUS. 77 



in which they were found, Pennant mentions that a man employed by the 

 farmer to capture them for manure earned for a considerable time four 

 shillings a day by selling them at the rate of a halfpenny a bushel. 



On the Continent the refuse is used for manure after the oil is extracted. 



The fighting instinct is limited to the males, and may be as well observed 

 in captivity as in nature. It is then that the use of the spines and the 

 armour becomes manifest, for on their skilful use the life or death of the 

 combatant depends. Sometimes the cause of battle is the desire to possess 

 a cave, or recess, or corner already occupied, but the sense of honour is so 

 delicate in these little fishes, that even a longing glance thrown towards a 

 spot which might become a happy home is sufficient to provoke an assault on 

 the passer-by. Or, if one fish has a position of vantage, and feels the presence 

 of less fortunate companions irksome, his spines and spears are at once erected 

 to drive the gazers away, saying, no doubt, with Horace, " Odi profanum 

 vulgus, et arceo/' The battle begins; the combatants swim round each 

 other rapidly, biting and thrusting, retreating and advancing, to avoid or 

 deal a blow. It is not often that the weaker seeks safety in flight, for he 

 knows that no quarter will be shown to the vanquished if captured. He 

 rather tries to act on the defensive until such time as the stronger fish shall 

 forget his discretion, and sooner or later the abdomen of the enemy will be 

 ripped up. When opponents are thus disposed of or driven away, the valiant 

 Stickleback, no longer worn with care, grows fat and increases in length. 

 And as the season advances he begins to construct a nest. According to 

 Professor Blanchard, the first step is the excavation of a depression on the 

 bed of the stream by a rotatory movement of the body, and then, as Monsieur 

 Costa had previously recorded, stalks of grass, rootlets of trees, and other 

 delicate fibres of vegetable matter, are laid in the hollow, and cemented to- 

 gether with mucus from the skin. Walls are then raised, and ultimately 

 roofed over, a small aperture only being left as an entrance. The nest is 

 nearly an inch in diameter. 



The male now puts on his most brilliant colours, and, conspicuous in his 

 scarlet breastplate, and sides shining with a glossy lustre, leaves his labours 

 and goes in search of a mate, by no means contenting himself with the first 

 female he sees; but selecting, with many caresses, one ready to spawn, he 

 allures her to the nest, and, should there be any indisposition to enter his 

 nest, something more than gentle pressure, it has been observed, is used to 

 force her into it. She enters, and in a few minutes deposits a few eggs, 

 and forces a way out on the opposite side and escapes. The male follows her 

 through the nest, and fertilises the eggs. Next day he again goes in search 

 of his mate, but the conjugal instinct is not very strong among Stickle- 



