130 GEO. S. HUNTINGTON 
of the extant mammalian forms, the lungs are asymmetrical 
organs, built on Aeby’s type II, with the eparterial development 
confined to the right lung. This enormous preponderance of 
the dominant mammalian type can only signify that this degree 
of pulmonary extension meets the respiratory demands of all the 
varied specific forms which operate under it, despite their mani- 
fold diversity in other structural directions, and is amply 
sufficient to carry them along their specialized developmental 
paths. | 
The exceptions above mentioned stand out clearly from among 
the great mass of the average forms. They are all associated 
with an increased respiratory demand to which the resulting pul- 
monary extension appears as the structural response. 
In contrast with these organizations typifying advance over 
average mammalian conditions, the small groups constituting 
Aeby’s fifth type of bilaterally symmetrical hyparterial distribu- 
tion, can only be interpreted as the remnant of an archeal mam- 
malian organization which has been in course of evolution re- 
placed by higher types of pulmonary development in the vast 
majority of living forms, but still persists in a few isolated in- 
stances and groups, as in J'axidea among the carnivores, and in 
some of the Hystricomorphs among the rodents. 
I believe that the contradictory discrepancy introduced into 
the problem of genetic kinship by the atypical pulmonary or- 
ganization of Taxidea as compared with all other mustelidae, of 
the Hystricomorphs in contrast to the remaining members of the 
entire rodent order, and perhaps in the cetacean exceptions men- 
tioned, finds its ultimate solution in the fact that the effects of 
environmental influence upon the vertebrate organization as a 
whole, must be judged separately by the results shown in the in- 
dividual components of the same. In other words ‘Environ- 
ment’ is a composite concept, comprising a large number of physi- 
cal factors, some of which are frequently antithetical to others 
in their influence on organic evolution. The vertebrate body is 
likewise a composite of a number of specific structures which, 
while they act as a unit in performing the offices of the organiza- 
tion as a whole, respond to their environment as individual parts 
