1. Ultrathin sections and macerated preparations of the sciatic nerves of adult mice have been examined with the electron microscope. Sections were prepared with a modification of the thermal expansion sectioning technique. Several fixatives were employed, and, of these, osmic acid proved best in researching the submicroscopic structures in the nerve fibers.
2. Exceedingly thin axon fibrils about 110 to 170 Å in diameter were observed in the axons. They were predominantly oriented in the long axis of the fiber and were apparently anastomosing with one another to form a network. Endoplasmic reticulum, from 600 to 1000 Å in diameter, was also found scattered throughout the axoplasm. They appear as tubular fibrils. Elongated narrow mitochondria,0.2 to 0.35μ in width, were also found in the axoplasm. Neurofibrils in the conven- tional sense are to be regarded as artifact caused by fixatiou.
3. A thin membrane, axolemma membrane in the conventional sense, was observed at the border between myelinated lamellae and axoplasm.
4. The myelin sheath was composed of a characteristic laminated structure which was observed as alternating concentric dark and light lamellae in thin section preparations. This structure was identical with the flexible lamellar structure, isolated single or in piles, in the fragmented preparations. The periodicity in the lamellar structure was measured by means of shadow casts as being of 140 to 170Å, corresponding to a shortened period brought about by drying. Schmid t-L ante r. mann incisures were also observed.
5. The myelin sheath was covered with neurilemma sheath consisting of a granular membrane, in average thickness of 400 Å. Mainly longitudinally arranged collagen fibrils were attached to this membrane. Sc hwann cell cytoplasm seems to continue to the neurilemma membrane.
6. Truly non-myelinated axons have been seen in the peripheral nerves. The contents of their axoplasm were similar to those of the myelinated fibers. Several non-myelinated axons were enclosed in the cytoplasm of a single Sch w an n cell and its outer limiting membrane.

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This comparative study was made on 34 different species of vertebrates,216 cases in all, from monkey to urodela.
The periodic acid-S chiff (PAS) reaction of blood cells, with and without the use of saliva, was examined, some in more detail than others. The presence or existence of the pigmented leucocytes in the streaming blood was simultaneously tested from the standpoint of comparative hematology.
As to the PAS reaction intensities of neutrophil leucocytes, the following three groups could be classified: firstly amphibian group, the strongest; secondly reptilian group, the moderate; and thirdly avian group, the weakest reactive group. The mammals generally indicated a wide variation ranging from the strongest group to the weakest group. Among these, however, the neutrophils of horse, toad and tadpole indicated a particularly intense reaction. The PAS reaction of human neutrophils was weaker than these, but stronger than the other mammalian, reptilian or avian groups. This relationship is somewhat different from the results of the peroxidase reaction where human neutrophils consistently indicated the strongest reaction in all kinds of vertebrates. Generally speaking, it was also noticed that there was a certain parallel in the glycogen and peroxidase reaction activities in the animal neutrophils, while not at all in the animal eosinophils.
The eosinophil leucocytes, whenever present, contained the PAS reactive substance in their intergranular or ground substance, agreeing with the localization of the alkaline phosphatase reaction. The PAS reactive substance of them was hardly digested by saliva as in the avian pseudoeosinophil leucocytes. Regarding the reaction intensities of the eosinophils, particular racial variations, namely, significant phylogenetical relations could not be found.
It is worthy of note that the glycogen content in the neutrophils of the cold-blooded vertebrates did not decrease even at the end of hibernation. Again it was interesting to find that the snake's blood platelets contained the largest clump of the PAS reactive substance, and that the rodents except guinea pig were generally characterized by the relatively weak PAS-reaction of the neutrophils. In short, as to the periodic acid-Schiff reaction, a continuous evolution of blood cells could not be found, and profound gap in the phylogenetical relationship was distinctly shown between mammalia and ayes.
The pigmented leucocytes in the streaming blood could be seen in the cold-blooded animals, while not in the warm-blooded animals. They were rarely found in lizards, frogs, toads, newts and salamanders, while frequently found in tadpoles. The pigmented leucocytes, if present, generally came to below 0.5 per cent of the whole leucocytes in each animal. They possessed the character of monocytes or polymorphonuclears, which phagocytosed a certain amount of the pigment granules, and indicated negative peroxidase reaction.

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In the present cytological and histological research, the normal glomeruli in fresh human kidneys from five healthy executed men were studied with special reference to cytological characteristics of the cellular elements of the glomeruli as well as histogenetical relationship between the surfacing cells (Deckzellen) of the glomerulus and the epithelial cells of the Bowman's capsule.
In the cytoplasm of the surfacing cells of the glomerulus a well developed net-like Golgi apparatus, a number of slender rod-shaped mitochondria, stainable granules and vacuoles are demonstrated, which facts suggest that these cells are provided with a secretory activity, sending secretory material into the cavity of the Bowman's capsule.
Among such ordinary (typical) surfacing cells, there occur in indefinite parts of the glomerulus variable number of peculiar surfacing cells with darker cytoplasm containing more numerous thicker mitochondria, numerous coarse stainable granules and vacuoles. On the basis of these cytological evidences it may be concluded that these atypical surfacing cells would play more active secretory function than the ordinary ones. It must be one of the noteworthy findings obtained in the present study that these atypical surfacing cells of the glomerulus are apparently identical with the atypical epithelial cells often found in the epithelium of the Bowman's capsule. In the author's previous study on the epithelial cells of the proximal convolution of the renal tobulus it was learned that these atypical epithelial cells of the Bowman's capsule epithelium are identical with the epithelial cells of the proximal convolution. All of these findings in both the present and the preceding investigations support the view that the lining cell layers of the three parts of the nephron are continuous and of the same origin, namely of epithelial nature. In the present study the author could actually confirm the continuity of the Bowman's capsule epithelium and the surfacing cell layer of the glomerulus.
Therefore it appears appropriate to designate the surfacing cells (Dec kzellen) of the glomerulus as“ visceral epithelial cells of the Bow ma n's capsule” against the conventional term, parietal epithelial cells of the Bowman's capsule.

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