102 GEO. S. HUNTINGTON 
This vesicle is surrounded by condensed mesenchyme and rep- 
resents, in d’Hardiviller’s opinion, the anlage of a separate lobe 
of the left lung. The pulmonary arteries descend symmetri- 
cally on each side, ventral to both the right eparterial bud and 
the proximal bud from the left stembronchus, and then turn 
dorsad to follow the dorso-lateral surface of the stembronchi. 
Both the right and left cranial buds turn dorsad after arising 
from their respective bronchi. Possessing identical origin, direc- 
tion, and relation to the pulmonary artery they appear as abso- 
lute morphological homologues. D’Hardiviller hence concludes 
that the lungs of the rabbit begin their development as bilater- 
ally symmetrical organs, the bronchial tree conforming to the 
bilaterally symmetrical eparterial form (Aeby’s type I*). The 
asymmetry is acquired during subsequent development. The 
right eparterial anlage continues to extend, but the left epar- 
terial vesicle becomes gradually reduced and finally disappears 
altogether. In an embryo of 13 days 8 hours he continues to 
find a vesicle attached to the cranial part of the left stembron- 
chus, but its walls have become greatly thickened. At 13 days 
15 hours the connection with the left stembronchus, hollow in the 
preceding stage, has been reduced to a solid pedicle, and at 14 
days there is left only a slight mesodermal condensation at the 
site formerly occupied by this ephemeral left eparterial bud. 
D’Hardiviller bases the following conclusions on the above 
alleged observations: 
1. In the rabbit each lung at first carries an eparterial branch 
of the stembronchus. The left eparterial bud follows for a 
short period the same course as the homologous bud of the right 
side. It then atrophies, disappearing entirely, and the two 
lungs, which were originally symmetrical, become secondarily 
asymmetrical. 
2. The three characteristic bronchial types established by 
Aeby in the mammalia have only a ‘secondary va'ue’ (Sic!). 
The important factor lies in the existence of an eparterial ele- 
ment on each side. This may persist in development, or atrophy 
on the left side only, or on both sides, thus giving rise to the 
three principal mammalian types, viz.: 
