How a chick gets in to its eggs

One day, a teacher took his pupils to a chicken farm to pay a visit. When they came near the incubator, chick just got out of its egg shell.

"It's wonderful to see a little thing come out from the egg shell, isn't it？" the teacher said.

##CONTINUE##"Yes, sir." said one of the boys, " but it would be more wonderful if we knew how a chick gets in to its eggs hell before hand."