212 The Outline of Science 



t rations arc not wanting of what might be called pretty pieces of 

 behaviour. Let us select a few cases. 

 The Stickleback's Nest 



The three-spined and two-spined sticklebacks live equally 

 well in fresh or salt water; the larger fifteen-spined stickleback 

 is entirely marine. In all three species the male fish makes a nest, 

 in fresh or brackish water in the first two cases, in shore-pools in 

 the third case. The little species use the leaves and stems of 

 water-plants; the larger species use seaweed and zoophyte. The 

 leaves or fronds are entangled together and fastened by glue-like 

 threads, secreted, strange to say, by the kidneys. It is just as if 

 a temporary diseased condition had been regularised and turned to 

 good purpose. Going through the nest several times, the male 

 makes a little room in the middle. Partly by coercion and partly 

 by coaxing he induces a female first one and then another to 

 pass through the nest with two doors, depositing eggs during her 

 short sojourn. The females go their way, and the male mounts 

 guard over the nest. He drives off intruding fishes much bigger 

 than himself. When the young are hatched, the male has for a 

 time much to do, keeping his charges within bounds until they 

 are able to move about with agility. It seems that sticklebacks 

 are short-lived fishes, probably breeding only once ; and it is rea- 

 sonable to suppose that their success as a race depends to some 

 extent on the paternal care. Now if we could believe that the 

 nesting behaviour had appeared suddenly in its present form, we 

 should be inclined to credit the fish with considerable mental 

 ability. But we are less likely to be so generous if we reflect that 

 the routine has been in all likelihood the outcome of a long racial 

 process of slight improvements and critical testings. The secre- 

 tion of the glue probably came about as a pathological variation ; 

 its utilisation was perhaps discovered by accident; the types that 

 had wit enough to take advantage of this were most successful; 

 the routine became enregistered hereditarily. The stickleback is 

 not so clever as it looks. 



