346 CHIKANOSUKE OGAWA 
nuclei in the cells of the intercapillary space le superficially 
and are not spherical. As already noted, they are round or 
elliptical in surface view, but in side view appear somewhat 
flat, the lower parts of the nuclei following the contour of the 
capillaries on both sides and sinking only slightly into the inter- 
capillary spaces (fig. 8). Thus it is obvious that the nuclei are 
situated superficially. In attempting to find out whether or not 
the cell bodies themselves are also superficial, I found that the 
hematoxylin-eosin method was useless, as eosin does not differ- 
entiate the cell body from the surrounding tissue. Then, for 
the purpose of differentiating underlying tissue from the epi- 
thelium, I used Mallory’s, van Gieson’s, and Bielschowsky’s 
methods. They also proved unsatisfactory. However, with 
Heidenhain’s iron-hematoxylin the preparations were obtained, 
which showed distinct differentiation and proved that the cell 
body dips only slightly into the intercapillary space, not reaching 
as far as the lower level of the capillaries (fig. 8). It is therefore 
evident that the large cells of the tortoise are quite flat, while 
the respiratory epithelium of Amphibia, including nucleated as 
well as flat portions, is not quite flat. This difference is more 
significant than may appear at first, as will be shown below. 
The difference becomes more obvious when we consider the 
snake and gecko, for here the intercapillary spaces are very wide 
and the large cells so flat, even in the spaces, that they can 
hardly be recognized in cross-sections. At times they are con- 
fined entirely to the interecapillary spaces; consequently it is 
here impossible to distinguish two portions, though it is possible 
in Amphibia. The respiratory epithelium of Mammalia consists 
of small, nucleated, and large non-nucleated cells and differs from 
Reptilia in that the flat cell of the latter has no nucleus. The 
phylogenetic development of respiratory epithelium may thus be 
summarized as follows: The respiratory epithelium, which con- 
sists of only one kind of cell in Amphibia, is divided into two 
kinds of cells in Reptilia, namely, nucleated, large, flat cell and 
cuboidal cell, the former being very flat compared with the cells 
of Amphibia. In Mammalia the epithelium consists of two kinds 
of cells, while the nucleus is lost in the flat cell. The develop- 
ment of the large, flat cell will be clear from figures 9, 10, and 11. 
