46 
SECOND BOOK. 
by fishes, but by other water animals, and so are 
the fry, as the newly-born fishes are called. 
9. “There is an important difference between fishes 
and the other backboned animals that I must not 
forget to mention,” added Mr. Johnson. “You 
remember that the hearts of mammals and birds 
have four chambers, while those ' of reptiles have 
three. Now a fish has a two-chambered heart, and 
in this way is distinct from all other backboned 
animals excepting the amphibians in their first 
stage of life.” 
INSECTS.— I. 
1. At their next visit to their friend, the naturalist, 
the boys found the tables filled with trays of lovely 
insects. It was indeed a grand display, and they 
were lost in wonder at the beautiful sight. 
2. “We now leave the animals with backbones,” 
said Mr. Johnson, “ and we come to those that have 
no bones — the Invertebrates, as they are called. 
Of these there are no less than five sub-king- 
doms. As I am not able to speak of all these sub- 
kingdoms, I have chosen a single class in one of 
them. 
3 . “In the cases and drawers which I have put out 
you see scores of different kinds of insects, some of 
them of wondrous beauty. With all their differ - 
ences of colour and shape, their bodies are all 
