In this country few studies on the water circulation in lakes have been made so far, although the current is one of the most fundamental factors in physical, chemical, and biological limnology. In Lake Biwa-ko, thirty-six years ago lake currents were surveyed by the staff of Kobe Marine Observatory with the aid of current-meter, afterwards Dr. HIDAKA carried out a series of model experiments. In the last summer, the present authors investigated the current of that lake by drift-bottle method.
On the occasion of the authors, limnological survey in Lake Biwa-ko last autumn, water temperature was observed in the surface and subsurface layers at about 100 stations. Sectional distribution of temperature was found to suggest the existence of water circulation of special mode : a strong thermocline, which developed over the entire lake at about 25 meters below the surface, was inclined or rose considerably as shown in Fig. 2. Remembering that the density of lake water is principally influenced by water temperature, deformation of thermocline should be considered to prove the existence of horizontal pressure gradient in the lake water.
In the present paper, the authors treat the water movement as geostrophic current in two layered waters divided by the thermocline, and for the determination of pressure distribution they draw the depth contours of thermocline corresponding to 15°C isothermal surface (Fig. 1). Current pattern in the upper layer along those contours indicates such directions that deeper contours lie on the right-hand side as the observer looks in the direction of flow, and current velocity is calculated by assuming that pressure gradient equals Coriolis force (taking centrifugal force in some rigions into consideration). In Lake Biwa-ko, two counter-clockwise swirls, velocity of which is about 16 cm/sec, are deduced from the procedures stated above.

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Lake Katanuma is a crater lake of the Volcano Katanuma in Miyagi Prefecture, Japan, and has been recognized by many limnologists for its high acidity (pH=1.9) due to sulfuric acid.
The fungi and the bacteria were very scarce in this lake compared with other harmonic and dystrophic lakes. The sulfur-oxidizing bacteria were only one species among the special group of bacteria. Penicillium citrinum was very common in the water as well as in the bottom mud. It was an only fungus inhabited this disharmonous water. No saprolegniaceous fungi could be found.
The toxic action of the lake water upon the microbes was studied under the laboratory conditions. The aquatic Phycomycetes could grow in the lake water diluted in 1/10. The spore of Penicillium citrinum isolated from Lake Katanuma could thrive for 7 months or more in the lake water, while that of Mucorales died out within a few days.

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The water colors of twenty ponds which were selected at random among the eighty ponds were measured by the new method mentioned already at every fifteen days. The mean of chromatic coefficient (x, y), brightness (Y), dominant wave-length (λD), and excitation purity (Pe) of the water colors of these ponds were calculated at every time in order to catch the tendency of seasonal change of water color. The mean of the chromatic coefficient is plotted on the C. I. E. chromaticity diagram (Fig. 1). The mean of the other values are shown in Figs. 2, 3, and 4, by which we can see the tendency of the seasonal change of algal population in the confidence limits of 95 per cent. The results obtained are as follows :
(1) The locus of point x, y, runs from April to November in nearly parallel with the spectralocus (Fig. 1). It may therefore be said that the change of the water color during this period is a change of the hue, not of the brightness and chroma.
The value of the dominant wave-length decreases gradually from 577 mμ during the period from April to July, and at the same time water colors change from yellowish brown to yellowish green through olive (Fig. 2), the value of the dominant wave-length increasing in the opposite way.
(2) The locus of point x, y, runs from November to March in nearly parallel with the isodominant wave-length's line (Fig. 1). It seems therefore that the change of the water color during this period is principally a change of both the brightness and chroma, not one of the hues of the water color ; and at the same time water colors change quickly from yellowish green to dark olive during the period from November to December, returning to yellowish green or pale olive till March (Figs. 1, 3, and 4).
(3) The dominant wave-lengths were distributed between 565 mμ and 579 mμ, mostly between 572 mμ and 574 mμ during the year ; accordingly, the water colors were mostly olive during the year. The value reached its maximum in April and at its minimum in July (Fig. 2).
The brightness is distributed between 7. 0 and 12. 0 per cent and the excitation purity is distributed between 31.0 and 44.0 per cent. The curve of the brightness is considerably similar to that of the excitation purity (Figs. 3, 4).
I have reported the same facts as a simple equation which denotes a positive correlation between the two values.
(4) In the seasonal change of confidence intervals in the means of the three values of water color, the values in August, September, and October, as well as in February and March are not so great as the values in the other months (Figs. 2, 3, and 4).
From these facts it is understood that the water colors in both summer and winter resemble one another and are not rich in varieties.
From the seasonal change of water colors, it will be possible to classify them into two categories, i. e. type A and type B, whose characteristics are as follows :
Type A : - In July the values of brightness and excitation purity of water color become low and locate point x, y, approaching the Illuminant C on the chromatological diagrams ; the water colors in this period show dark olive. Such water colors are ordinary found in winter. Therefore, in the ponds of this type, dark olive coloration of water occurs twice during the year, in June and December (Fig. 5).
Type B : - The low value of brightness, excition purity, and dark olive coloration occur only once during the year, i. e. in December (Fig. 6).

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1. By using the radioisotope Ca⁴⁵, the pathway of calcium flux was investigated in the crucian carp, Carassius carassius (L.) and a marine teleost, Duymaeria flagellifera (VALENCIENNES).
2. The medium in which the experimental fish was placed was isolated from the fish body in enclosing its posterior half with a rubber sac (fig. 1). For the observation of Ca⁴⁵ uptake, Ca⁴⁵Cl₂ was added to one of the separated media. In the excretion experiment, the fish was first placed in Ca⁴⁵ solution to let it take up the isotope and then transferred to non-isotopic medium.
3. The pattern of Ca⁴⁵ uptake by the crucian carp seems to indicate that the Ca influx is made mainly through the gills and fins. In the case of crucian carp, when the anterior body is exposed to the medium containing Ca⁴⁵, a considerable accumulation of Ca⁴⁵is observed in the scales not only of the anterior body but also of the posterior body which is not directly exposed to the isotopic medium. On the other hand, when the posterior body is exposed to the isotopic medium, the accumulation by the posterior scales is apparently small even in the direct exposure to Ca⁴⁵and that by the anterior scales is much smaller. These results may indicate that the uptake of Ca⁴⁵ is much greater through the gills than that through the fins in the posterior body.
4. In the marine fish, D. flagellifera, the pattern of Ca⁴⁵ uptake is remarkably different from that by the crucian carp. The amount of Ca⁴⁵ uptake through the posterior body is nearly the same as that through the anterior body. This result may suggest that the Ca influx across the fins in this marine fish is much greater as compared with that in the crucian carp.
5. In the crucian carp, the amount of Ca⁴⁵ excreted through the anterior half of the body is roughly equal to that through the posterior half.

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The new localities of a freshwater Caloglossa have been found in Japan, i, e. Shiroshima (land-tied island), Kumanoguh (22 km. distant from, 5 m. high above the sea), Hakenomiya (20 km. distant from, 16.5 m. high above the sea), Katohda (37.5 km. distant from, 15 m. high above the sea), Bunda (38.539.5 km. distant from, 15 m. high above the sea) and Kamio (27 km. distant from, 12 m. high above the sea). Though Shiroshima springs are situated close to the sea-shore, they belong to freshwater (Cl content : 12 mg./l).
The dispersal of Caloglossa ogasawaraensis in freshwater areas has been explained as either by the regeneration of fragments which were carried by waterfowls from the sea (negative migration) or by the adaptation of plant which has moved gradually to freshwater areas along the streams (positive migration). The former is expected to be more actual than the latter.
The writer considers that, at the above-described localities, Caloglossa has survived in freshwater since these alluvial districts were up-heaved to land from the sea. But these migrations can be explained by the negative migration because the plant is considered to be moved to the neighbouring freshwater areas along the course of water.

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1. A freshwater pond on the cape Ose-zaki in the Izu peninsula, Middle Japan showed the chlorine contents 296.46 mg/l in July and 238.32 mg/l in November, the values being about 1/60 of that of the sea water. Such low chlorine contents of this pond lying near the sea seem to be due to its source of water which is fed mainly by the subterranean water.
2. There were found thirteen species of phytoplankton and a few species of zooplankton. The most abundant phytoplanktonts were Navicula sp. in July and Kirchinelliella lunaris and Cosmarium sp. in November. Among the zooplankton, Mesocyclops leuckarti and Diaphanosoma brachyurum were predominant in July and Bosmina longirostris in November. All the plankton species were of freshwater, no brackish water species being found.

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