334 CHIKANOSUKE OGAWA 
Previous histological researches, concerning the respiratory 
spaces of the lung, have been confined to a limited number of 
animals, without much consideration of the whole vertebrate 
system. In this paper I have endeavored to shed further light 
on these problems and to add to the information we already 
have. 
I wish to extend my heartiest thanks to Prof. B. Suzuki for 
much valuable advice. I am also deeply indebted to Prof. R. R. 
Bensley and Dr. G. L. Streeter for their courtesy in placing at 
my disposal the facilities of their departments while translating 
this paper. 
MATERIAL AND METHODS 
The materials used for the present study are as follows: 
Amphibia: Diemyctylus pyrrhogaster, Rana nigromaculata, 
Megalobatrachus japonicus 
Reptilia: Clemmys japonicus, Gecko japonicus, Elaphe quadri- 
virgata. 
Aves: Columba livia, Gallus domestica, Anas, Passer. 
Mammalia: Talpa, Vesperugo, Epimys, Cavia cobaya, Lepus 
cumiculus, Capra, Felis domestica, Canis familiaris, Homo. 
In this: investigation the following were used for fixation 
purposes: 
Ten per cent formol, formol alcohol, potassium bichromate, 
sublimate, Miiller-formol, and Flemming’s solution. Silver 
nitrate was used to impregnate the intercellular substance. <A 
description of the technique is omitted here as it is given under 
each chapter. 
RESPIRATORY EPITHELIUM 
1. Respiratory epithelium in Amphibia 
For the study of the respiratory epithelium of Amphibia, 
the lungs were first injected with a 0.25 per cent solution of 
silver nitrate and then cut open and spread out. When the 
cement substance had become dark the pieces were mounted. 
In the case of Rana and Megalobatrachus, the tissue which had 
been impregnated in this way was also imbedded in celloidin 
