384 CHIKANOSUKE OGAWA 
to this, I find that the fibers often pass over the capillaries. 
Besides the fiber system which [ have mentioned in the preceding 
animals, there is, according to Russakoff, a fine circular fiber 
system around the alveolar capillaries. I recognize the same cir- 
cular fibers in the lungs of Amphibia and Reptilia, but I find in 
Mammalia and the human there is a different condition. Here, 
when the somewhat thick fibers pass from one: intercapillary 
space to another, the fiber divides sometimes into fine fibers which 
either continue as such into the other intercapillary space or are 
again gathered into a single thick fiber (fig. 36). In this branch- 
ing, the fibers may pass over one side of the capillary only or 
they may split and pass over both sides, but in all cases their 
course is One approximately at right angles to the axis of the 
capillary. In short, the fibers of the capillaries are connected 
with the fibers in the intercapillary spaces and thus belong to 
the same system. Perhaps Russakoff saw only these fine fibers 
in relation to the capillaries and concluded that they formed a 
separate system. I was unable to detect the fine reticular fibers 
on the capillaries in the lungs of the mole and bat, but in the 
rat these were indicated, although the technique did not allow 
confirmation. 
B. The reticular fibers of the embryonic mammals. Russakoff 
observed in the 32-em. new-born that the reticular fibers arise 
from cells in the alveolar walls, pursue a slightly tortuous course, 
and anastomose with each other. He also states that these 
fibers are in connection with fine fibers which form close nets 
beneath the epithelial cells. I was unable to see any special nets 
of subepithelial fibers in different stages of the rabbit embryo. In 
addition it was seen that in the embryo the fibers in the alveolar 
walls are less coarse, less tortuous, and form looser nets than in 
the adult (fig. 38). In the embryo, as in adult animals, the fiber 
rings of the alveolar ducts and alveoli are thicker than those of 
the alveolar walls. 
The degree of staining of the reticular fibers does not vary with 
age as it does in the case of elastic fibers. 
C. The relation between elastic fibers, reticular fibers, and mus- 
cle fibers in regard to position. Russakoff describes the relation 
