DEVELOPMENT. 205 
velopment of the common Crab, so different is the out- 
ward form of the newly hatched embryo from that of the 
adult, that the former has been described as a distinct 
species. 
The most remarkable example of metamorphosis among 
Vertebrates is furnished by the Amphibians. A Tadpole 
—the larva of the Frog—has a tail, but no legs; gills, in- 
stead of lungs; a heart precisely like that of the Fish; a 
horny beak for eating vegetable food, and a spiral intes- 
Fie. 173.—Metamorphosis of the Newt. 
tine to digest it. As it matures, the hinder legs show 
themselves, then the front pair; the beak falls off; the 
tail and gills waste away; lungs are created; the digest- 
ive apparatus is changed to suit an animal diet; the heart 
is altered to the Reptilian type by the addition of another 
auricle; in fact, skin, muscles, nerves, bones, and blood, 
vessels vanish, being absorbed atom by atom, and a new 
set is substituted. /oulting, or the periodical renewal of 
epidermal parts, as the shell of the Lobster, the skin of 
the Toad, the scales of Snakes, the feathers of Birds, and 
