126 GEO. S. HUNTINGTON 
from the remaining members of their respective groups is found 
in their intrapulmonary organization. This raises the important 
question, what is the evolutionary significance of cardinal diverg- 
ence in the bronchial architecture and what its value as a genetic 
character in determining phyletic kinship? 
To take the example of Taxidea as a concrete case in point. 
The zoological group of the mustelidae, in which Tazidea is 
included, is derived by Prof. Gregory from the lower oligocene 
Plesictis. Considering the facts obtaining in the modern descen- 
dants of this common ancestral form the Reduction Theory would 
hold that the Plesictis-lung has already developed the dominant 
mammalian type with the retention of the dextral eparterial bron- 
chus, and the same had been transmitted unchanged to all of the 
modern descendants, with the single exception, as far as known, 
of Taxidea. In this form further pulmonary reduction otcurred, 
resulting in the phylogenetic loss of the right eparterial lung- 
segment and the acquisition of the tracheal bulla. It is diffi- 
cult to conceive of environmental changes, capable of inducing 
this reduction, and confined in their operation to Taxidea, to 
the exclusion of the other mustelidae. The supposition assumes 
the existence of morphogenetic factors which we find nowhere 
in the mammalian series. I do not know of a single instance of 
even a probable reduction of a formerly developed pulmonary 
segment in a mammalian lung. The phylogenetically acquired 
metameric reduction of the trunk cavity in mammalia, with its 
incidental effect on the pleural space, would in itself negative this 
assumption. The inclusion of the right cardiac lobe in the 
phrenicomediastinal angle of the right lower lobe in man and 
some other mammalia, is merely the result of the closure of the 
pericardiophrenic space following pericardiac fixation to the 
diaphragm. The morphological status of the lobe is maintained 
by the cardiac branch of the right stembronchus. 
If d’Hardviller’s alleged discovery of an ephemeral left epar- 
terial bronchial vesicle in the embryo of the rabbit had been 
confirmed, it would point far more directly to an attempt on 
part of the left lung to acquire additional respiratory territory 
than to the evanescent appearance during ontogeny of a pul- 
