PULMONARY EVOLUTION IN MAMMALIA 107 
It is thus hardly possible in these observations of d’Hardiviller and 
Bremer that we are dealing with a true regressive process. In fact, 
it is more probable that in both cases we are either dealing with a 
variation or a dorsal bronchus which is placed higher up than usual 
upon the stembronchus. This assumption is made quite probable by 
, 
Bremer’s statement that his eparterial bronchus did not supply the apex 
of the lung. 
I can endorse this conclusion absolutely. Through the cour- 
tesy of Professor McClure I have had the opportunity of studying 
and reconstructing the lungs in two uterine embryos of Didel- 
phis and in one uterine embryo of Dasyurus, contained in the 
embryological collection of Princeton University. No trace of a 
left eparterial bronchus was found in any of these. While these 
embryos and their reconstructions will be described and figured 
fully in a more extensive forthcoming publication dealing with 
the morphological details of the marsupial lung, I append here 
two views of the model of the bronchial tree and pulmonary 
artery in the 10 mm. uterine embryo of Didelphis marsupialis. 
The architectural pattern of the lung conforms entirely to the 
dominant placental type, with the anlage of the eparterial bron- 
chus restricted to the right side. The left stembronchus does 
not carry a corresponding component, but is entirely hyparterial 
in its distribution. After giving off its cranial eparterial deriva- 
tive (Hp.) in the typical situation the right stembronchus carries 
three well developed ventro-lateral hyparterial bronchi and the 
less far advanced anlage of the fourth (V'-V*). The cardiac 
bronchus, with three laterals and the expanded end bud, is 
derived from the ventro-medial aspect of the right stembronchus 
at the level of the caudal margin of V'. The left stembronchus 
gives origin to four ventro-laterally directed hyparterial bron- 
chi (V'-V*), slightly less far advanced than the corresponding 
uds of the right side. The Ascending Branch (A) of left V1 
extends craniad to the level reached by the eparterial component 
of the right side. Each supplies the homologous apical portion 
of its lung. There is no indication of a left eparterial bud. 
The series of the dorsal bronchi contains four distinct compo- 
nents on each side (D'—D*‘), 
