174 DARWINISM AND THE PROBLEMS OF LIFE 



buries itself in the mud ; the bullhead expands its 

 gill-covers so that the spines stand out ; the perch 

 elevates its spine-fin, and in the stickle-back the spines 

 are raised in a fixed joint so that it does not lower its 

 weapons even after death. In this way it is safe from 

 most enemies ; only the salmon and torsk can swallow 

 it with impunity. It can also protect its young. The 

 male, which is the more lively of the two sexes in this 

 species, and reveals every emotion by a pretty play of 

 colour, builds a nest of root-fibres and vegetable matter 

 which he glues together with a sticky substance that 

 oozes from his sex-opening. Then, by a show of colour, 

 by graceful movements, and, if that does not avail, by 

 pushes, he induces a female to lay its 68-80 eggs in the 

 nest. When that has been done, the male seeks other 

 females to fill up his nest ; and when he thinks he has 

 enough eggs, he improves the nest, and watches it most 

 carefully. Every creature that comes near is furiously 

 driven off; these are generally of his own species, as 

 they have a great liking for the eggs. His watchfulness 

 doubles when the little stickle-backs appear. They swim 

 away over and over again, and he brings them back in 

 his mouth, and puts them back in the nest. He does 

 not relax his care until the young can easily support 

 themselves, and then he leaves them. 



The bullhead also defends the eggs and the young 

 for some time, and the way the Rhodeus amarus takes 

 care of its young is most peculiar. This is one of the 

 prettiest of German fishes on account of its graceful 

 movements, and the male has also such glowing colours 

 in the spawning season that the whole animal seems to 



