RESPIRATORY SPACES OF THE LUNGS 379 
seven to ten fibers. It was concluded that these fibers extend 
all the way around the capillary, although this conclusion could 
not be absolutely verified because the stroma stained very deeply. 
These fibers very seldom anastomose with each other. These same 
fibers are seen also in the larger capillaries and appear to form 
a continuous system in the lung. The fibers in the subepithelial 
connective tissue are somewhat thick and spread out flatly 
(fig. 30). Although a careful search was made, no fibers could 
be seen passing over capillaries, also no circular fibers were seen 
around the muscle fibers, as in the tortoise. 
Elaphe quadrivirgata. An appearance similar to that in Gecko 
was seen, except that the subepithelial fibers are somewhat finer. 
Aves. The domestic fowl and duck were used in this study. 
There are bundles of reticular fibers, slightly wavy, around the 
flute-holes. In the respiratory canaliculi the reticular fibers 
are exceedingly fine and twine themselves around the capillaries, 
but they do not encircle the capillaries as they do in the gecko 
and snake (fig. 31). 
2. Reticular fibers in Mammalia 
A. Reticular fibers of the adult mammals. The reticular fibers 
in the adult mammals are in general similar in arrangement to 
the elastic fibers. 
Talpa (mole), Vesperugo (bat). The reticular fibers of the 
walls of the bronchioli continue into the walls of the alveolar 
ducts where they encircle the mouths of the alveoli (fig. 32). 
The fibers also form rings around the mouths of the alveolar 
ducts. A majority of these rings are composed of a single fiber, 
but some are made up of several fibers. These rings in turn 
send fibers into the walls of the alveolar ducts where they form 
rings around the alveolar mouths. The alveolar mouths in the 
first part of the alveolar ducts sometimes consist of several fibers, 
but further down the ducts the mouths have only a single fiber 
in the ring. In both the mouths of the alveolar ducts and the 
alveoli the fibers of the rings show a regular wavy or spiral wind- 
ing. The fibers of two adjacent rings around alveolar duct 
