194 GEO. S. HUNTINGTON 
In a series of 29 examples of Hrinaceus europaeus recorded by 
Narath (Le., p. 181) 20 specimens carried only the usual right- 
sided eparterial bronchus, but in 9 individuals there was a 
bilateral eparterial development. 
These are examples of exceedingly variable species, with un- 
stable bronchial organization, but the same conditions obtain to a 
greater or lesser degree throughout the mammalian class. They 
are instances of the selection by the primitive entodermal anlage 
of developmental lines of bronchial budding which are atypical 
for the species concerned, although typical for some other forms. 
Their appearance as mutations is rendered possible through the 
universal plasticity of the embryonal anlage. Thus the primitive 
lung-tube, with the typical plan of its unfolding determined by 
heredity for each species, yet retains the archeal potency of devel- 
oping bronchial anlagen from any point of its entodermal lining, 
and is hence able to produce in the individual both minor depar- 
tures from the regular type, and cardinal variants which alter 
the morphological character of the bronchial tree, as in the in- 
stances cited. 
IT. Physiological factors operative in pulmonary evolution. The - 
outstanding fact in all vertebrate pulmonary evolution is the 
increase in structural complexity and the resultant heightened 
functional activity of the cranio-ventral as compared with the 
more archeal caudal lung segments. This distinction begins to 
appear far back in the reptilian stem. It is well defined in the 
higher lacertilian lung, becomes dominant in the paludal and 
marine chelonia and reaches its highest development in the 
crocodilia. It is a pronounced factor in the organization of the 
avian lung, modified by the peculiar morphogenesis of the organ 
in this class, and forms the guiding line, as above detailed, in 
the interpretation of the mammalian pulmonary evolution. 
Selection bases the morphogenesis of the organ on the univer- 
sal adaptability of the primitive promammalian entodermal 
lung-sae to respond to the functional demands made on it. This 
inherent potency derived from the mammalian ancestry to de- 
velop bronchial buds from any points of its epithelial surface, 
and to assemble them into a pattern adapted to the respiratory 
