RESPIRATORY SPACES OF THE LUNGS Be 
a large number of epithelial cells he together in an intercapillary 
space, the cells in the center may not come in contact with the 
capillaries, so that they have no flattened surfaces and are per- 
fectly cuboidal. Among these cuboidal cells exceedingly small 
ones are sometimes seen. 
Although the blood-capillaries are of almost the same caliber 
throughout the lung, they may be twice or three times as thick 
as usual where they branch from arteries or veins. Over these 
thick blood-capillaries the flat portions of the cells may become 
greatly extended or the capillaries may be covered by epithelial 
cells which are totally flattened. The latter, not being in con- 
nection with the intercapillary spaces, show no differentiation 
into two portions, but have the appearance of endothelium. 
Rana nigromaculata. The respiratory epithelium of Rana 
differs only slightly from that of Diemyctylus (fig. 2). 
My results agree on the whole with Elenz’s description of the 
respiratory epithelium of the frog. There are only a few state- 
ments to be added. 
While in Diemyctylus the flat portion of the respiratory 
epithelium only occasionally spreads from one intercapillary 
space to a neighboring one, in Rana this is almost always the 
ease. The epithelial cells, which are located in an intercapillary 
space, number from one to four or still more, but usually there 
is only one. The respiratory epithelium shows no morphological 
difference in relation to its location in the lung, the cells at the 
base of the alveoli being like those of the septum. This is also 
the case in other amphibians and reptiles. 
Megalobatrachus japonicus (giant salamander). The respi- 
ratory epithelium of Megalobatrachus is also essentially like 
that of Diemyctylus (fig. 3). The capillaries and intercapillary 
spaces are somewhat wider than those of Diemyctylus. Some- 
times very small intercapillary spaces lack nucleated portions 
of cells entirely. Such pictures are not as rare as in Diemyctylus. 
The thicker blood capillaries are here also covered by wide flat 
portions of the respiratory epithelium, but I did not find any 
case in which totally flattened epithelial cells covered such 
blood-capillaries. 
