PULMONARY EVOLUTION IN MAMMALIA 153 
the statement in accordance with the migratory theory as fol- 
lows: ‘Die Keimzellengruppe der Apicalknospe kann bei friih- 
zeitigen Wachsthum ins Gebiet der Trachea gedriingt werden 
zu einer Zeit, wo sich die Lungenanlage schirfer abgesondert 
hat von der Trachealanlage.” These words convey no morpho- 
genetically conceivable idea. There exists no developmental 
agency capable of ‘pushing’ a group of proliferating cells out of 
contact with the epithelial layer, as a part of which they develop, 
and transferring them from a point on the future stembronchus 
to a point on the future trachea, where they are to be invaginated 
between the already existing cells of that locality to function as 
the anlage of the tracheal eparterial bronchus. This is a migra- 
tory reductio ad absurdum. After all a developing bronchial 
bud is not to be regarded in the same light as a metastatic deposit 
from a neoplasm. To read Narath further, ‘‘Wenn uns auch die 
Ontogenese keine Aufschliisse gibt fiir das ‘Hinaufwandern’ des 
apicalen Bronchus, so muss dieselbe doch nach den zahlreichen 
vergleichend anatomischen Thatsachen unzweifelhaft in der Phy- 
logenese stattgefunden haben.” 
We have above carefully considered the ‘numerous comparative 
anatomical facts’ (p. 141). Comparative anatomy if correctly 
interpreted absolutely negatives the migratory theory and teaches 
that a branch budding from any point of the bronchial tree de- 
velops at the site of its first inception. 
Narath concludes his brief ontogenetic consideration of this 
vital question with the rather naive statement: ‘‘Es scheinen 
mir Thiere mit hoch auf der Trachea sitzenden apicalen Bron- 
chien wie Schaf, Rind, Schwein fiir das Studium nicht recht 
geeignet zu sein.” They certainly are not ‘suitable for this 
study’ if it is intended to use them in support of the vagaries of 
the migratory theory. 
The cranial lobe of the typical right artiodactyl lung far ex- 
ceeds the corresponding element of the opposite organ, extending 
across the median line and actually in many species fitting over 
the apex of the left lung. The peripheral respiratory area re- 
sulting from the unfolding of a terminal bronchiole is practically 
a constant value in each mammalian form. Increase in the 
