PULMONARY EVOLUTION IN MAMMALIA 137 
Especially in comparing the right and left lung of type II* 
does the physiological and topographical correspondence between 
the right eparterial trunk and the ascending branch of the first 
left ventral hyparterial bronchus impress itself in the above sense 
on the observer. The two bronchi supply equivalent districts of 
their respective lung and agree in many forms so closely in the 
details of their secondary derivatives, that the impulse, as 
Narath puts it, is almost irresistible to regard the right eparterial 
trunk as having, in some way, become separated from its original 
parent stem, the right first ventral hyparterial bronchus, and 
moved dorso-craniad upon the stembronchus to a varying dis- 
tance ahead of the main pulmonary artery, while its homologue 
of the left lung retains its archeal origin from the first left ven- 
tral hyparterial bronchus, appearing as its ascending branch. 
As soon as this idea has acquired concrete form and expression 
in the terms ‘splitting off’ (Abspaltung, Ablésung) and ‘migra- 
tion’ (Emigration, Ueberwanderung, Abgebung) of bronchial ele- 
ments, it at once dominates the entire concept of bronchial archi- 
tecture and its mode of evolution. Not only do all the main 
types find their ready interpretation as various phases of the 
process of ‘migration,’ if the same is once accepted, but all 
variants within a type, the occurrence of accessory bronchi, in 
fact any and all departures from the usual pattern, are only so 
many additional proofs in substantiation of this hypothetical 
method of bronchial evolution. A term conveying easily visual- 
ized mechanical changes has here been made to take the place 
of critical analysis of the actual morphogenetic processes involved. 
When we turn to the two sources alone directly available, com- 
parative anatomy and ontogeny, for corroborative evidence in 
support of this theory of bronchial migration, it is either alto- 
gether wanting, or it flatly contradicts the theory. The crux of 
the entire question is not so much the exact point occupied in a 
given type by a given bronchus, but how did it attain that lo- 
cation in the course of phyletic or ontogenetic development. 
Let us examine some of the details of the problem more closely. 
At the outset it will become apparent that the theory, if car- 
ried back to its logical starting point, will bring us to a novel con- 
