英文科学读本 第三册·Lesson 35 More about the Fish

Lesson 35 More about the Fish

I want you to think again about the fish and its breathing, Norah, said Fred. "It gets its air from the water. Now it is quite clear that it cannot get as much air in this way as lung-breathing animals can. We live and move about in an ocean of air itself. Now just tell me how you feel when Will and I give you a good long 'pepper' with your jumping-rope."

I get out of breath and very hot; I breathe very rapidly, said Norah.

That's quite right, said Fred. "You then breathe in more air than usual. Our bodies are always warmer or colder according to the amount of air we breathe in."

Fishes take in so little air by their gill-breathing that it is not enough to warm their blood or their bodies. They are always cold. We call them coldblooded animals.

Teacher showed us, said Willie, joining in, "that this is why fishes are never clothed in wool, fur, or feathers, or even with a thick hide. They have no heat in their bodies to keep in, and they have no need of a thick warm coat."

That's right, Will, said Fred. "I wanted to talk about their clothing next. Think of the herring and its shiny silvery-looking coat. But the coat kept coming off on my fingers while I was showing you the herring's gills, Norah."

What do you mean, Fred? asked Norah. "Do you mean those little round scales that you had all over your hands? Are they the herring's coat?"

Yes, they are. Teacher says the fish is really encased in a coat of mail. Next time you see a fish, run your finger along its body from head to tail, and you will find it very smooth; then run it back again to the head, and the scales will ruffle up.

Each scale is fixed into the skin in front only; the rest of the scale is loose and overlaps the next one behind it. As the fish moves through the water every scale is pressed closer and closer to its body, and there is nothing to hinder its movements.

Why, that's almost exactly like the feathers on the bird's body, said Norah. "They all point backwards, so that the bird shall have nothing to hinder its flight through the air."

That's a good girl, said Fred. "Now I will tell you one thing more about the coat of the fish. You know if you take a fish in your hand it feels slimy and slippery. Teacher says the fish sends out over its body a slimy oil, which helps it to glide smoothly and easily through the water."

SUMMARY

Fishes have cold blood, because they can take in only small quantities of air by means of their gills. They do not want a warm coat. Their clothing is formed of scales. Each scale is fixed into the skin in front only. The scales overlap one another, press close to the body, and help the fish in its movements.