THE FISH 



Fishes move through the water much as birds do through 

 the air, easily, buoyantly, and gracefully. They swim with 

 their tails, balancing and directing themselves with their fins. 

 The swim-bladder reduces the exertion of keeping afloat; 

 the resistance of the water is reduced by their slippery scales; 

 and the fish is helped forward by the closing in of the water 

 behind the wedge-shaped body. Fishes were the first animals 

 with jaws and a back-bone. It is no wonder, then, that they 

 have grown, through these long ages, to fit their environ- 

 ment as perfectly as any living form. 



Small fish may be kept in aquaria, especially if they be 

 supplied with water plants and pond scum, which by giving 

 off oxygen, and taking in of carbon dioxide, keep the 'balance* 

 between the oxygen used by the fish and the carbon dioxide 

 given off by them. Fish should be fed very little, and pro- 

 tected from the hot sun. Very rarely, however, can fish be 

 made to breed in an aquarium. The conditions are so 

 unnatural that the sensitive reproductive organs remain 

 dormant. 



Lessons from Fish Roe 



The scientist, however, with his microscope, may observe 

 something of what takes place in the preparation of the male 

 and female germ cells of either plants or animals, their union, 

 and the formation of the new individual. The ripe eggs and 

 sperm cells of plants, and the ova and sperm masses of the 

 lower animals, especially of fish and poultry, are readily seen. 

 From these and from the records of science, we may piece out 

 the story of reproduction. 



Since fish cannot be bred in aquaria, the roe, or egg masses, 

 of female fish, together with the greatly distended sperm sacs 

 of the male, obtained at the market in season, will help to 

 focus attention while the story is told of the way fish live, 

 lay their eggs, fertilize them, and of the way the young grow. 



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