"PERFECT-MOUTHED" FISHES 227 



fishes, or Gunnels (Pholis gunnellus), common on our seacoasts, 

 behave in this more friendly and equitable manner ; both male 

 and female remain with the eggs and take charge of them 

 alternately, coiling themselves round the mass, which thus 

 becomes rolled and pressed into a compact ball. Finally, the 

 Butter-fishes deposit the ball of eggs in a hole in a rock, 

 usually choosing one that has been bored by the little rock- 

 boring mollusc pholas, and it is said that both parents remain 

 near the spot to guard and protect the eggs until the young are 

 hatched. 



Of the fishes that build nests for the reception of their eggs, 

 the little Three-spined Stickleback (Gastrosteus aculeatus) is one of 

 the most familiar examples. 1 " The nest is a really remarkable 

 structure. The male stickleback first makes a small depression in 

 the sand or shingle at the bottom of the pond, and in this places 

 tiny pieces of weed and fibre to make a soft resting-place for the 

 eggs, and over all he spreads a silken coverlet, formed frojm a natural 

 secretion that the male stickleback possesses, mingled with par- 

 ticles of fine dust or sand. When the nest is completed, the little 

 stickleback, in all the glory of his courtship colouring, goes forth 

 to seek his lady-love and lead her to the nest. He soon finds out, 

 however, that the old adage that you may lead a horse to the 

 water but cannot make him drink unless he is so disposed applies 

 equally well to his mate, who, although quite willing to observe 

 the nest he has built, shows at first considerable reluctance to 

 enter it ; and it requires all the perseverance and powers of per- 

 suasion of the excited little male fish to induce her to enter and 

 deposit her spawn. At last, however, the female stickleback goes 

 into the nest, but directly she has deposited her spawn therein 

 she emerges and departs, leaving to her little mate all the anxious 

 and responsible duties of looking after the eggs until the young 

 emerge and can fend for themselves. The male stickleback takes 

 up the burden of his duties quite cheerfully, and tends his precious 

 charge with the greatest devotion, never straying far from the 

 nest until the young are hatched. All day long he mounts 

 guard, attacking and driving away any unwelcome visitors who 

 attempt to approach, and keeping up a constant and vigorous 

 fanning with his fins at the entrance to the nest, thus causing 



1 " The Nature Book." F. Martin Duncan. 



