248 BRITISH FRESHWATER FISHES 



and is attached to the bottom by means of sand and 

 pebbles ; its completion takes several days, and 

 when finished it is usually a barrel-shaped struc- 

 ture, often an inch or more in diameter and with an 

 opening at one end ; sometimes it is dome-shaped, 

 with the aperture at the top. 



So far the fish has been intent upon his work, 

 only trying to provide against any interruption to 

 its progress and watching with suspicion every 

 creature that approaches ; now he devotes his 

 energies to attracting a mate, whom he guides to 

 the nest, swimming round her with evident pleasure 

 and driving her in by thrusting at her with his 

 snout, or, if she be unwilling, even using his spines. 

 When the female has entered she lays a few eggs 

 and then bores a hole through the wall of the nest 

 on the side opposite to the entrance, and departs ; 

 immediately after the eggs are laid the male enters 

 the nest and fertilizes them. On the following day 

 he goes in search of another spouse, and this is 

 repeated until the eggs are sufficiently numerous. 



At this time of courtship and matrimony the 

 males are violently jealous and often indulge in 

 fierce duels, the two rivals rushing at each other, 

 dealing violent strokes with their pelvic spines, and 

 then hastily returning to the neighbourhood of their 

 nests ; after a few rounds one gives in and then the 

 victor indulges in a splendid display of colours, 

 whilst those of the vanquished become dull; these 

 fights are often mortal, one combatant frequently 

 ripping his opponent open with his sharp spines. 



When the spawning is over the male guards and 

 protects the eggs, furiously attacking any other 

 Stickleback that may approach ; with his mouth he 



