RESPIRATORY SPACES OF THE LUNGS Boo 
and cut into thin sections. In general the respiratory epithelium 
of the amphibian lung is more easily impregnated than that of 
Reptilia and Mammalia. Besides these preparations, controls 
were made by staining sections and also some of the uncut tissue 
with ordinary dyes, such as hematoxylin and eosin. 
Diemyctylus pyrrhogaster. According to Elenz, the respiratory 
epithelium of Triton (a genus closely related to Diemyctylus), 
consists of large, flat cells, whose nuclei are also large and are 
always located in the intercapillary spaces, joining each other on 
the capillaries. I was able to recognize a similar condition in 
Diemyctylus (fig. 1). 
The blood-capillaries of the lung of this animal are only wide 
enough to admit of the passage of one blood-corpuscle at a time. 
In some other animals, which will be mentioned later, the capil- 
laries are so wide that two or three blood-corpuscles can pass 
along side by side. The intercapillary spaces are of varying 
widths, but they are usually of a somewhat larger caliber than 
the capillaries. 
For convenience in the deseription we may distinguish two 
parts in the respiratory epithelial cell, one of which is located 
in the intereapillary spaces and holds the round nucleus, while 
the other spreads out flat over the capillaries. These will be 
called, respectively, the ‘nucleated’ and ‘flat’ portions. 
In surface view the epithelial cell presents a pentagonal or 
hexagonal form. The flat portion is extremely thin and can 
not be seen in transverse sections of the fixed material, while 
the nucleated portion, which has the same width as the capillary, 
reaching inward to the stroma, generally has a cuboidal form, 
though its thickness differs in different parts of the lung, some- 
times becoming almost flat. 
As a rule, the flat portion appears more extensive in surface 
view than the nucleated portion, but in exceptional cases the 
former covers the capillaries only partially and is consequently 
smaller than the latter. Occasionally the flat portion stretches 
out over the capillaries and reaches the neighboring intercapillary 
space. In rare cases a small intercapillary space may have no 
nucleated portion and is covered only by the flat portion. When 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 27, NO. 3 
