390 CHIKANOSUKE OGAWA 
5. The non-nucleated cells of mammalian respiratory epi- 
thelium cannot be considered as parts of the nucleated cells, 
though some authors are inclined to believe so. 
6. The respiratory epithelium of the rabbit embryo in early 
stages consists of a single kind of cuboidal cell, and as develop- 
ment proceeds and comes nearer to the final stage, some of them 
become flatter. In the final stage the respiratory epithelium of 
all the alveoli consists of a mixture of the two kinds of cells 
without respiration. The flat cells become flatter at the begin- 
ning of respiration. Disappearance of the nuclei of flat cells 
takes place in the final embryonic stages and occurs, not suddenly, 
but gradually by processes of pyknosis, karyorrhexis, etc. The 
greater part of the nuclei probably has disappeared before 
parturition. 
7. Reparation and regeneration of non-nucleated flat cells 
seem to be brought about by extension of small nucleated cells 
and disappearance of nuclei. 
8. The muscle fibers of the lung appear isolated in Diemyctylus 
japonicus and grouped in Megalobatrachus japonicus, while in 
Rana nigromaculata and Clemmys japonicus there are both kinds 
of appearance. The muscle fibers of Elaphe quadrivirgata and 
Gecko japonicus form mostly bundles. 
9. The muscle fibers are entirely absent in all parts of the 
- alveolar ducts in the bat lung. There are existent some circularly 
arranged muscle fibers at the mouths of the alveolar ducts in 
the mole, rat, guinea-pig, rabbit, goat, cat, dog, and man. In 
the mole and guinea-pig the muscle rings are sometimes absent 
at the mouths of the periphery of the ducts. There are no muscle 
fibers around the alveolar mouths in the lungs of the mole, rat, 
rabbit, and goat, while in the lungs of the dog and man muscle 
fibers are demonstrated in some of the alveolar mouths and in 
the lung of the cat the greater number of alveolar mouths show 
fairly strong fibers. Muscle fibers in the alveolar walls are very 
seldom demonstrated in the cat, dog, and man, but they are 
not found in the other mammals before mentioned. 
10. The elastic fibers of the mole and bat form a weak ring 
around the mouths of the alveolar ducts and alveoli. From 
