84 Lessons in Nature Study. 



The fish does not swallow the water, but merely allows 

 the water to pass through so as to wash the dark-red fringes 

 of the gills. That keeps fresh water near the gills all the 

 time, and so the impure matters of the blood, escaping into 

 the water from the gills, are quickly washed away. Pure 

 oxygen in the water enters the fish's blood through the 

 gills and purifies it. 



If we will leave the fish in this water a long while, he will 

 begin to pant, or move his gills very fast. He will come to 

 the surface and swim about restlessly. That is because the 

 water has lost most of its free oxygen. If we did not change 

 the water, the fish would soon die. Why do not fishes in 

 the brooks and ponds die ? The plants growing in the 

 water take up the impure matters and give off oxygen to 



FIG. 20. 



the water, and fishes give to the plants just what they need 

 for their food. 



Scrape off a scale from the fish. See the little socket 

 where it grew. See the markings like those on a shell ; 

 notice how they lap over each other like the shingles on a 

 roof. See how nicely nature made the fishes to swim in the 

 water. How easily their narrow pointed bodies cleave the 

 water. 



Let us now see how a fish is built up. Here is a skeleton. 

 See the parts of the backbone (vertebrae). Count them, and 

 also count the ribs. The fish has a backbone (spine), as 

 we have. Note how it joins the skull. See how carefully 

 nature protects the spinal cord by its position, (It is not 



