2i6 THE INFANCY OF ANIMALS 



these he promptly fertilises. When the nest is at last 

 full he mounts guard over the entrance, and stays at his 

 self-imposed sentry-duty for nearly a month, defending 

 his precious charge with great spirit against all comers. 

 Curiously enough, the most dangerous of such assailants 

 are his own wives, for commonly more than one female 

 seems to be induced to spawn in the nest. They would, if 

 they could, devour every single egg. But his work is not 

 confined to keeping out marauders ; since to ensure 

 the successful hatching of the eggs he seems to be obliged 

 from time to time to change their position in the nest, 

 and to keep them constantly bathed in fresh water. This 

 last he contrives to do by driving a stream through the 

 nest by means of a fanning motion of the breast fins and 

 the tail. 



When the fry at length appear, his vigUance is still 

 further taxed. For in addition to defending his ofispring 

 from predaceous fishes, including his own kind, he has 

 to guard and restrict the activities of his brood. If 

 they stray too far from the nest he seizes them in his 

 mouth and gently expels them into the zone of safety 

 again. Soon, however, his task lightens, and his vigilance 

 relaxes : indeed, it seems probable that death puts an 

 end to his labours, for it is beUeved that the adults die 

 at the end of their first breeding season. 



The spotted goby, or pole-wing, which occurs in the 

 Thames, for instance, is a nest-builder. Here, however, 

 an old cockle-shell is made to do duty for a nest. The 

 shell is placed with its concavity downwards, beneath 

 which the soil is removed and cemented together, it is 

 said, by a special secretion of the skin. Access to the 

 nest is gained by a cylindrical tunnel, and the whole 

 nursery is covered by loose sand. Here again, the male 



