How does the Centipede get to be so big?

Centipede swallowed three of the little green crystals, the old man's gift to James.

‘Very peculiar,’ the Centipede said. ‘Very, very peculiar indeed. Let me tell you what happened. I was messing about in the garden under the old peach tree and suddenly a funny little green thing came wriggling past my nose. Bright green it was, and extraordinarily beautiful, and it looked like some kind of a tiny stone or crystal…’
‘Oh, but I know what that was!’ cried James.
‘It happened to me, too!’ said the Ladybird.
‘And me!’ Miss Spider said. ‘Suddenly there were little green things everywhere! The soil was full of them!’
‘I actually swallowed one!’ the Earthworm declared proudly.
‘So did I!’ the Ladybird said.
‘I swallowed three!’ the Centipede cried. ‘But who’s telling this story anyway? Don’t interrupt!’