The results are shown in Fig. 1 and 2. In the case of Motosu-ko, an oligotrophic lake, any essential difference cannot be noticed between MIYADI'S data obtained in 1930 and the present ones in 1953. But in the case of Syôzi-ko, an eutrophic lake, changes towards a greater degree of eutrophy seem to have occurred during the twenty years since MIYADI'S observation.

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In recent years the problem most often encountered in groundwater investigations has probably been that of predicting fluctuations of water levels or flows to be caused by future withdrawals of groundwater. But, THIEM'S or THEIS' method cannot be applicable to those problems in multiple-well system always producing abundant flow of groundwater. Mathematical method giving pumping effect in uniformly leaky aquifer is applied to such systems and some notable results are obtained. For example, when a well is pumped by the rate of Q in multiple-well system, of which one side is bound by free water and the other is assumed infinite.The increase of total yield from this system is given by Qe-√b/Td, where T and b are coefficients of transmissibility and leakage, and d is distance from free water to the pumped well. This exponential factor can be easily obtained by the analysis of tidal fluctuations in such an aquifer, which were presented by the author as p₀e-√b/Tx sin wt, where tidal change in sea level is assumed P₀ sin wt and x is the distance from the sea. Then, the total flow in this system except the new withdrawal by pumping is predicted to be decreased by Q (1-e-√b/Td).

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The staff of our laboratory made a collection of both plankton and epiphytic micro-organisms on Utricularia in a swamp located closely west to Lake Tôro-ko, where the limnological survey was carried out on the same day (23^rd August 1957). This swamp is situated between the lake and the River Kushiro, which is mean-dering about in the peaty district. There is only a narrow route, through which even an Ainu-canoe can scarcely pass. The water-weed (Utricularia japonica) was so densely growing on the route-side that a canoe could not go out of the route.
(1) Considerable lots of rotatorian species were identified among the specimens. Twenty-three kinds of rotifers were found in the plankton samples, and eighteen species were recorded from the epiphytic samples, and they became thirty-two species in total. Besides them, there were found a few rotifers, which could not determine to species.
(2) Nine species were in common from both samples ; eight of them, excepting Keratella cochlearis, were the creeping rotifers. All of ten epiphytic rotifers, which were not found in the plankton samples, were creeping species. On the other hand, six out of fifteen species, which were observed only in the plankton samples, belonged to swimming members.
(3) Most of the rotifers determined were the common species. Lecane ligona (DUNLOP) was recorded for the first time in our country. The typical form of Brachionus quadridentatus was found in the samples taken among Utricularia, and brevispinus-form of the same species was detected also in the plankton samples.
(4) In addition, the zooplankton of Lake Tôro-ko itself were very poor, notwithstanding the enormous phytoplanktonts occurred.

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