PARENT AND OFFSPRING 115 



disc-fish, whose " male, after fertilizing the eggs, 

 carries them in his mouth to a little floating nest of 

 air-bubbles which he has already blown upon the 

 surface." In some instances the male shows his care 

 only by mounting guard over the eggs wherever they 

 happen to be laid. In the butterfish (Fig. 41) the 

 male and female take turns in protecting the eggs 

 by coiling their bodies around the mass, until the 

 young are hatched. 



FIG. 41. BUTTERFISH AND EGGS. (After Holt.) 



(From " The Infancy of Animals," by W. P. Pycraft) 



Perhaps we may take as the next step in evolution 

 the construction of nests for the young; for even 

 among the fish, generally regarded as so dull, such an 

 elaborate instinct is found. As a rule, this is per- 

 formed by the male fish alone, but there are some 

 instances of both parents uniting in this labour. We 

 have an example in the American bowfish: both 

 male and female participate in the making of the 

 nest, which is formed by clearing away the reeds and 

 making a shallow depression at the bottom of the 

 pool, in which the eggs are hatched. The young are 

 jealously guarded by the male, who keeps the swarm 

 together. 



The common stickleback supplies us with the most 



