42 
SECOND BOOK. 
gill -slit. Under it you plainly see the thin flat 
gills lying closely over each other. Notice how 
beautifully fringed they are.” 
9. “And red too!” exclaimed William. 
“Yes. They are red because they are full of 
little blood-vessels, which are placed just where 
they can be well-bathed by the water on its way 
out. Then some of the air in it can pass into the 
blood within the tiny vessels and purify it. 
10. “Now look at the covering over the fish. It is 
the very best kind it could have for passing easily 
through the water.” 
“ Fishes have scales for a covering,” said William. 
“Yes. Pass your hand from the head to the tail 
of this fish.” The boys did so, and the fish felt 
quite smooth. 
11. “ Now pass it along the opposite way,” said 
Mr. Johnson. In doing so the boys could plainly 
feel the small scales, and some of them came off on 
their hands. They were nearly round, and were 
thin and hard. 
12. “ The scales are fixed only in front,” said Mr. 
Johnson, “ and each one laps over the one behind 
it, in something like the way a bird’s feathers over- 
lap each other. They are of different shapes in 
different kinds of fishes, and are often marked with 
fine lines, which cause them to glow with beautiful 
colours.” 
13 . “ One day Arthur and I went fishing,” said 
