154 GEO. S. HUNTINGTON 
respiratory surface spells a corresponding increase in the number 
of the terminal bronchioles. It is a simple mathematical propo- 
sition to prove that the number of the ultimate bronchioles and 
the consequent area of the respiratory surface will depend, with 
the same type and ratio of division of the bronchial tree, upon 
their caliber and upon the distances separating the origins of 
the primary conducting tubes from the stembronchus. 
Thus in the case of the right eparterial bronchus (A) the extent 
of its respiratory area is in direct ratio to the distance X—Y sep- 
arating it from the next adjacent derivative (B) of the stembron- 
Fig. 6 Schema of bronchial and tracheal derivation of right eparterial 
bronchus. A., eparterial bronchus; B., first ventral hyparterial bronchus. 
chus, the first ventral hyparterial branch. In comparing the 
dominant type (fig. 6°) with that obtaining in the artiodactyls 
(fig. 6°), the enlarged respiratory capacity of the latter is meas- 
ured by the greater length of the line X—Y. 
The phyletic as well as the ontogenetic interpretation of the 
migratory theory would hold that the tracheal eparterial bron- 
chus in the ancestors of the modern artiodactyls was a branch of | 
the first ventral bronchus, which in the course of evolution ‘emi- 
grated’ from this primitive site craniad, first onto the stembron- 
chus, and then still further in the same direction beyond the bifur- 
cation a variable distance up along the right side of the trachea. 
