PROBLEM I. The Kinds o^' Ani'inals of the Earth 



17. Report on the best treatment for snake bites. 



18. Frogs and toads make excellent subjects for night photography. 

 Use a flashhght to find them, open the lens of your camera, and then 

 burn a photoflash bulb. The flash lasts about one fiftieth of a second. 

 The lens is closed afterward. 



Fishes 



19. Use a natural history such as Hegner's Parade of the AiYmial King- 

 dovi or copies of the National Geographic Magazijie to learn more about 

 fish and their relatives, the sharks. Prepare a short talk. 



20. Have you ever maintained an aquarium of tropical fish? If you 

 have, report briefly to your class on their structure and habits. Could 

 you start an aquarium? 



21. Look up lungfish. Tell your classmates why biologists consider 

 them important. 



39 



The Invertebrates 



Animals without backbones. You know 

 that invertebrates have no backbone. 

 Whatever skeleton they may possess is 

 either on the outside, like a coat of 

 armor, or is so different from the skele- 

 ton of the backboned animals that you 

 M^ould never confuse the two. And while 

 all vertebrates are assigned to a single 

 phylum the kinds of invertebrates are 

 so varied that they are arranged in dif- 

 ferent phyla. Zoologists are not all in 

 agreement on just how many phyla the 

 invertebrates should be divided into. 

 However, all classifications include the 

 nine important phyla we will study. In 

 the diagram on page 40 there are draw- 

 ings of one representative of each of 

 these nine phyla. From the many thou- 

 sands of possible kinds these nine were 

 chosen: a grasshopper, a snail, a starfish, 

 an earthworm, a hookworm, a planaria 

 (a relative of the tapeworm), a jellyfish, 

 a sponge, and an ameba. In this book only 



a very few of the thousands of species 

 of invertebrates can be described. There 

 are about 800,000 species of inverte- 

 brates in contrast with the 40,000 species 

 of vertebrates. 



Fig. 48 This circle graph will help you com- 

 pare the mmibers of species of invertebrates and 

 vertebrates. It will also help compare the num- 

 ber of species of insects with the total mimber 

 of all other kinds of invertebrates. There are 

 approximately 40,000 species of vertebrates and 

 800,000 species of invertebrates, of which 600,000 

 are insects. 



