86 FOUR-FOOTED AMERICANS 



6. MoUusks. . . . Shell Fish, such as Oysters, Clams and Mussels, 



Snails, Slugs, Cuttle Fish, etc. 



7. Crustaceans . Animals covered with a hard shell, having 



many legs and a pair of feelei'S, oi- autennje, 

 breathiug through gills the air that is dis- 

 solved in the water. Lobsters, Crabs, etc., 

 are Crustaceans. 



8. Spiders and (Called Arachnidte, from Arachue, the Spinner, 

 Scorpions . . because they spin webs.) Are a sort of 



cousin tij Craljs, but live on the earth instead 

 of in tlie ■water. 



" The top branches of this group contain the Insects, 

 with many legs, their bodies being divided into three 

 jiarts. Insects go tlirough many changes in the course 

 of development. Take the butterfly as an example. 

 First an egg is laid by a fully grown butterfly ; second, 

 a caterpillar is hatched from the egg ; third, the cater- 

 pillar spins itself into a chrj^salis, or cocoon, out of 

 which comes the winged butterfly. Ants, mosquitoes, 

 flies, and beetles are all insects. 



" Among the next circle of branches we find the ani- 

 mals having backbones, the Vertebrates. I think you 

 will feel more at home M'ith them, and we ai-e more 

 nearly concerned with them now, as our mammals be- 

 long in this order, although there are many things you 

 must some day learn of the many backboneless twigs, 

 especially about the insects with their Avonderful wings 

 and stings." 



" I suppose my Rattlesnake is a rather low-down Ver- 

 tebrate, Uncle Roy," said Nat. 



"No, my boy, there are two grades below him and 

 two above. See," — and the Doctor drew a branch 

 with five divisions. 



