1.   It retained water and yet had subtle membranes which permitted air to penetrate and facilitated waste disposal of the embryo.

2.   Arctic air will penetrate southward across the Plains, sending a big chill as far south as Oklahoma and Texas.

3.   Bitter cold air will penetrate into Montana and North Dakota with temperatures falling toward zero later in the day.

4.   Grilled windows allowed the fresh air to penetrate the house.

5.   Look for spots where air is penetrating your house and work on closing all the gaps.

6.   Meanwhile, scattered thundershowers will erupt near the eastern Gulf coast where cooler air from sea breezes penetrate inland.

7.   Sometimes the warm moist air penetrates through the wallboard into the wall cavities.

8.   The forecast indicates that cold Arctic air will not penetrate very far south.

9.   When cold air penetrates one end of the country, it forces warm air to the other side.