PULMONARY EVOLUTION IN MAMMALIA 147 
Of all the characters cited by Narath the only ones that hold 
good are No. 5, the pulmonary artery relation, and No. 11, the 
relation of the monotreme pulmonary veins. Yet Narath him- 
self is most emphatic in denying to the vascular supply of the 
lung any morphological significance in the interpretation of the 
bronchial tree. He quite correctly sees in the arrangement of 
both pulmonary arteries and veins nothing but a close adapta- 
tion to the intrapulmonary architecture, the vessels fitting them- 
selves into the interbronchial spaces between the developing 
buds. 
Comparative anatomical evidence in support of the Migration 
Theory goes by the board altogether. 
ee Let us examine the ontogenetic evidence, with which the last 
word must rest in any case. 
For this Narath turns to one source where definite determin- 
ation is either extremely difficult or not at all obtainable, viz., 
the embryo of a mammalian form in which in the adult the right 
eparterial and first ventral hyparterial bronchi arise in close 
proximity to each other from the right stembronchus. In many 
forms included in this type the open interval between these two 
primary bronchi barely suffices in the adult for the passage of 
the main trunk of the right pulmonary artery in its ventro- 
dorsal course across the lateral surface of the stem-bronchus. In 
these types (and Narath’s chief examples, Echidna and Lepus, 
belong to this group) the earliest anlagen of the primary bronchi 
of the right lung appear in the form of slight swellings of the prim- 
itive lung-tube, grouped closely together and gradually shading 
into the adjacent. entoderm of the future stembronchus. At 
this stage there exists as yet no clear differentiation between the 
stembronchus and its primary derivatives. It is not possible to 
delimitate accurately the central tube against the faint swellings 
denoting the first buds of the future bronchi in question and of 
these anlages against each other. The attempt to do so results 
merely in an expression of the observers personal judgment and 
affords no proof either for or against their confluent or discrete 
origin, because the bed from which they arise, the future stem- 
bronchus, has not yet declared its definite limits. It is held by 
