Left-sided diaphragmatic hernias were created in 9 rabbit fetus at 23-26 day’s gestation

and were returned to their original amnioaic sac for further development until the 29 days’ gestation for cesarrean section to obtain living fetus. During the creation of the diaphragmatic hernias

13 normal fetus at a littet with the operated fetus were taken for morphological study of the stages of lung development. Electron microscopic obser vations in 9 diaphragmatic hernias demonstrated marked delay in the development of alvesli and at term the lung had small

thick-walled terminal air spaces with few cappillaries and no true alveoli when compared With the thinwalled alveoli in normal lungs. Another striking feature was an appearent increase in the frequency of type 11 albeolar. cells in diaphragmaric hernia lungs. Furthermore

the delay in the develoment of alveoli was more marked at 23 days’ geslation to creat the hernia than at later days