DEVELOPMENT 



cut the gum. The " splint bones " in the horse's foot 

 are undeveloped metatarsals. 



Animals differ widely in the degree of development 

 reached at ovulation and at birth. The eggs of frogs 

 are laid when they can hardly be said to have become 

 fully formed as eggs, since they undergo still further 

 change in the water. The eggs of birds are laid when 

 segmentation is far advanced, while the eggs of mam- 

 mals are retained by the parent till after the egg stage 

 is passed. 169 Ruminants and terrestrial birds are born 

 with the power of sight and locomotion. Most carni- 

 vores, rodents, and perching birds come into the world 

 blind and helpless ; while the human infant is depen- 

 dent for a much longer time. 



I . Metamorphosis 



Few animals come forth from the egg in perfect con- 

 dition. The vast majority pass through a great variety 

 of forms before reaching maturity. These metamor- 

 phoses (which are merely periods of growth) are not 

 peculiar to insects, though more apparent in them. 

 Man himself is developed on the same general principles 

 as the butterfly, but the transformations take place 

 gradually. The coral, when hatched, has six pairs of 

 partitions ; afterward, the spaces are divided by six 

 more pairs; then twelve intermediate pairs are intro- 

 duced ; next, twenty-four, and so on. The embryonic 

 starfish has a long body, with six arms on a side, in one 

 end of which the young starfish is developed. Soon the 

 twelve-armed body is absorbed, and the young animal is 

 perfectly formed. Worms are continually growing by 

 the addition of new segments. Nearly all insects 

 undergo complete metamorphosis, i.e., exhibit four dis- 

 tinct stages of existence egg, larva, pupa, and imago. 



