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1. 1. Innervation of the heart by the cardio-inhibitory nerve was electrophysiologically examined in Ligia exotica. 2. 2. Three kinds of cardio-regulatory impulses, one inhibitory and two acceleratory, were identified in each of the two anterior cardiac nerves. 3. 3. The inhibitory impulses induced inhibitory postsynaptic potentials (IPSPs) in all the six neurons comprising the cardiac ganglion and suppressed their spontaneous burst activities. 4. 4. The inhibitory impulses induced inhibitory junctional potentials (IJPs) in the myocardial cells and hyperpolarized their membrane potentials. 5. 5. We concluded that the cardio-inhibitory nerve innervates directly both the cardiac ganglion cells and the myocardial cells.

1. 1. Effects of evoked impulses in cardioregulatory nerves on the heart rate were observed in the crab, Sesarma dehaani. 2. 2. The nerve m has two regulatory fibers; one is inhibitory and another is excitatory. After longitudinal splitting of the nerve m, the stimulation of anterior part shows a decrease of the heart rate and that of the posterior part increases it. 3. 3. Stimulation of the nerve I only increases the heart rate. 4. 4. The nerve fibers could be categorized physiologically by different thresholds for the intensity of stimulation required for activation or by the change in stimulated portion of the nerve. 5. 5. Conversely, by the stimulation of single fibers, the nerve were analyzed in relation to the stimulation frequency and the resulting heart rate.

1. 1. Coordination of activities between the auricle and ventricle was studied in the heart of oysters. 2. 2. The auricles and ventricle possess different rates of intrinsic rhythms, and auriculo-ventricular (A-V) delay varies among preparations. 3. 3. The ventricular beat, depending on its moment in the auricular beating cycle, has prolonging or shortening effects on the beat interval of the auricle and vice versa. 4. 4. Stretching is suggested to be the mediating factor of the coordination by which auricle and ventricle accelerate and inhibit each other according to the beat moments in the beating cycle, to obtain a coordinated beat.

1. 1. Mediating factors of co-ordination of rhythms between the auricle and ventricle and the effect of a brief stretch on the electrical activity of the myocardium were studied in the heart of oyster. 2. 2. The co-ordination was maintained even in the state where only mutual stretching between the auricle and ventricle was kept and no electrical connection was found between them. Thus it was assumed that the co-ordination is mediated by mutual stretching without direct interactions in their electrical activities. 3. 3. A brief stretch altered the periodic membrane potential changes of the myocardium and caused prolongation or shortening of the beat interval depending on the moment of its application. 4. 4. Mechanism of the co-ordination of rhythms mediated by mutual stretching between the auricle and ventricle was discussed in relation to the positive and negative chronotropic effects on the beat interval by the brief stretch.

5, KJ00000602491, P

1. 1. The Ligia cardiac ganglion which is composed of six similar-sized neurons has been studied electrophysiologically. 2. 2. Intracellular recordings from the ganglion cells show periodic burst activity with conspicuous pacemaker potentials between bursts. 3. 3. All of the ganglion cells burst almost simultaneously and produce compound action potentials in the ganglionic trunk and the ganglionic nerve branches. 4. 4. The burst discharge is not always initiated in the same cell, but changes during spontaneous activity. 5. 5. When isolated, any of the ganglion cells could produce periodic burst activity with pacemaker potentials. 6. 6. Intracellular stimulation applied to one of the ganglion cells changed the burst interval and reset the burst rhythm of all ganglion cells. 7. 7. In Ligia heart, all ganglion cells have the pacemaker activity and may be mononeurons to the heart. These are compared to the properties of neurogenic hearts of some other crustaceans and Limulus.

Vertical distribution of dissolved oxygen and chlorophyll in summer-autumn season were determined in the offshore of Osaka in Lake Suwa. In mid-summer, when whole the surface of the lake was covered with blooming Microcystis, dissolved oxygen in the surface water layer could attain over-saturation to the utmost extent (160%). Late in August the amount of dissolved oxygen markedly decreased less than 90% saturation, in spite of a large amount of Microcystis existed. It might be related to the declining of the photosynthetic activity of the alga. Moreover, if drifting of the upper water containing a great part of Microcystis by wind (Susu-mizu) occurred, serious decrease of dissolved oxygen (less than 50% saturation) was observed. Wind and waves usually were not favorable to increase oxygen into the surface water. In such a situation carps cultured in the floating nets may be exposed to clanger of asphyxia unless a large amount of dissolved oxygen is supplied from surrounding water outside of the nets during the night. There was a relationship between the pH value and the saturation percentage of dissolved oxygen in the water of 0 to 2 m depth., Article, 信州大学理学部紀要 2(2): 139-148(1968)

Predation of mosquito larvae, Culex pipiens, by the guppy, Lebistes reticulatus PETERS, which has been recently acclimatized in hot springs in Japan, was studied under various experimental conditions. 1. Guppies could not survive in water of 35℃ and over, or at 10℃ and less. 2. At 25℃ guppies showed maximum predation of mosquito larvae. Adult guppies ate 21-91 mg of fourth instar larvae in 24 hours. These amounts correspond to 10-36 larvae in number when the larvae average 2.5 mg in weight per individual. At 30℃ the amounts of mosquito larvae eaten by adult guppies decreased from that at 25℃, but the decrease was less than that at 20℃. At 15℃ guppies ate few larvae and almost ceased growing. As a rule the quantity of larvae eaten by male guppies was less than that by femals. 3. Guppies could eat mosquito larvae in darkness as well as in light, though some decrease in amount of predation was observed. 4. Guppies ate mosquito larvae even when daphnids were available. There was slightly greater preference for daphnids than for mosquito larvae., Article, 信州大学理学部紀要 1(2): 79-92(1967)