Frogs and Toads 



is a useful member of goby society ; he builds the nest, 

 repairs it when necessary, guards the eggs and sees to it 

 that fresh supplies of water reach them, and he does so 

 in this manner : near his front door he takes up his 

 position and, with machine-like regularity, waves his fins 

 so that a continuous current of water passes over his 

 eggs. This is a common habit with many fishes, having 

 as its object the prevention of stagnant water collecting 

 round the eggs. 



The bitterling rises superior to nest-building ; it prefers 

 a living incubator for its eggs, in the shape of the common 

 pond mussel. By one of those curious coincidences 

 which are so common in nature that they point to a well- 

 ordered scheme of things, the breeding seasons of the 

 bitterling and pond mussel coincide. For this reason 

 they are able to help one another, though they certainly 

 do not do so wittingly. 



The bitterling, be it said, lays very few eggs. Were it 

 as prolific as the ling, which deposits twenty-eight millions 

 of eggs at a sitting, it would be hard on the pond mussel, 

 as we shall see. 



The mother bitterling deposits her eggs in the gaping 

 valves of a pond mussel shell ; there they remain, hatch 

 and pass the early stages of their development into fishes. 

 At the time the mother bitterling comes along it so 

 happens that the young pond mussels are seeking some- 

 one to take them abroad into the world ; they cannot go 

 themselves, they need someone to carry them. What 

 more natural, then, than that they should cling on to the 

 mother bitterling and be carried by her to new quarters ? 

 We have described the habits of these young pond 

 mussels elsewhere, so we need not discuss the question 

 here ; the advantage to the bitterling and pond mussel of 

 attending to their parental duties at the same time is 

 obvious. 



The wrasses, noted as being the only fishes known to 

 go to sleep, lying on their sides as they do so, build 



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