10 



A FEW FACTS ABOUT ZOOLOGY. 



may have seen the various stages in a silk-worm. First an 

 egg ; then, when hatched, a little worm called a larva, whose 

 whole existence is spent in feeding and rapid growth; then 

 it wraps itself in a cocoon and enters the pupa state, remain- 

 ing apparently dead till new organs are developed, when it 

 emerges a perfect winged insect, or imago. These are the four 



Fig. 6. 



stages — egg, larva, pupa, and imago. In Fig. 6 you see these 

 changes as shown in the mosquito. In the picture there is no 

 apparently dead pupa, but you may see the pupa-case, which, 

 being opened, is floating like a boat upon the water, and 

 supporting the mosquito in its efforts to escape. Many a 

 pupa-case upsets, thus drowning its occupant before he has 

 a single chance to try his wings. The pupa of butterflies is 

 unprotected, and is generally suspended by a single thread; 

 the pupa-case is generally ornamented with golden spots, 

 hence the name, chrysalis. The pupa of moths is inclosed 

 in cocoons. 



The Vertebrates. 

 We come now to the highest branch of the animal kingdom 

 — that to which we ourselves belong — the vertebrates. Every 

 vertebrate has a backbone ; every vertebrate has a solid 

 arch above that backbone, and a solid arch below it, form- 

 ing two cavities — no matter whether these arches be of hard 

 bone, of cartilage, or even of a softer substance. In the 



