460 WILLIAM SNOW MILLER 
Oppel, discussing the above statements of Renaut, says that 
the simple and compound lungs of vertebrates are homologous 
structures inasmuch as they all arise originally from the foregut 
which possesses the property of producing the respiratory epi- 
thelium. The uni-alveolar lung of Proteus, as well as the com- 
pound lobular lung of the highest vertebrates, considered as a 
whole, corresponds to this original lung. Though a single al- 
veolus of the highest vertebrates may correspond to the lung of 
Proteus in structure and function, qualitatively, both cannot eas- 
ily be homologized; rather an alveolus of the lung of the higher 
vertebrates corresponds only to a part of the lung of Proteus. 
The profuse division to which the perfecting of the respiratory 
apparatus has led in higher vertebrates has necessitated the sub- 
division of the originally single organ into numerous small unit 
regions. As a result of this division, varying in manner in dif- 
ferent species of animals, we have the origin and varying struc- 
ture of the bronchial tree. 
THE BRONCHIAL TREE 
Aeby, in his work on the bronchial tree, based on comparative 
anatomical studies, denies that the older idea of a dichotomous di- 
vision is the correct one. As the result of his studies he found 
the method of branching to be strictly monopodial: each bron- 
chus retaining its individuality to its end and sending off lateral 
branches. 
Ewart, in his work on the bronchi and blood vessels of the 
human lung, arrives at a very different conclusion from Aeby. 
He believes in dichotomy; not the even dichotomy of the older 
authors, but uneven dichotomy. 
Although I do not agree with Ewart in the mode of bronchial 
division, I must call attention to what seems to me to be a gen- 
eral misunderstanding as to his position. He is usually quoted 
as asserting that dichotomy is ‘‘The Alpha and Omega of bron- 
chial division.””’ True, he did make this statement; but that is 
not all of it. What he did say is: ‘‘The further dissection is 
carried within the lung, the less rarely does even dichotomy 
