PULMONARY EVOLUTION IN MAMMALIA 149 
embryo of Tarentola, gives the following account of the develop- 
ment in the remainder of the lung: 
Die iibrigen kleineren Blasen, welche die ganze tibrige Flaiche des 
primitiven Lungensackes bekleiden, sind auch nicht regellos umher- 
gestreut. Sie sitzen n&imlich in transversalen Reihen, welche rings 
um den Lungensack laufen,.und machen so den Eindruck von einer 
Art Segmentierung desselben (Figg. 10 und 11, v. tr.). Die Segmen- 
tierung ist in der mittleren Partie der Lunge am deutlichsten ausge- 
prigt. Die transversalen Reihen alternieren im grossen und ganzen 
mit den grossen dorsalen Blasen, so dass eine solche Reihe dem Zwisch- 
enraum zwischen zwei Blasen entspricht. Indes ist diese Alternation 
nicht besonders deutlich. Viele der Blasen zeigen eine Tendenz zur 
Teilung in zwei kleinere, gleich oder ungleich grosse Tochterblasen. 
In the attainment of the mammalian type the number of these 
successive rows is greatly reduced, and the interval between ad- 
jacent rows correspondingly increased, in conformity with the 
laws governing peripheral alveolar expansion. At the same time 
the number of the individual buds composing a row becomes 
likewise greatly diminished. This is especially evident in the 
cranial lung segments as compared with those occupying a more 
caudal level. Primary as well as accessory buds of any row, 
which later become defined as the ventral, dorsal, and accessory 
bronchi of their pulmonary segment, cannot be definitely ana- 
lyzed in their relation to the stembronchus until the latter has 
itself become clearly defined. The central common lung-tube 
or pulmonary cavum cannot be considered as the strict equivalent 
of the formed stembronchus until the primary buds have clearly 
differentiated themselves and declared their value and their re- 
lations to each other and to the line of the stembronchus. The 
first anlagen of the stembronchus and of its primordial deriva- 
tives are parts of a continuous and uniform whole, as the entire 
anure lung is in its adult form. When they can once be accur- 
ately delimitated they do not further change their mutual rela- 
tions by ‘migration.’ 
Narath (33, p. 281) sums up his conclusions regarding the 
development of dorsal bronchi in rabbit embryos as follows: 
Ich widmete also der Bildung der dorsalen Bronchien ganz besondere 
Aufmerksamkeit. Leider stésst die Untersuchung auf grosse Schwier- 
