Tthe effect of the population density on the occurrence of the dimorphic features in a cricket, Scapsipedus aspersus WALKER is reported is this paper. In the present cricket there are the macropterous form (M-form) and the brachypterous form (B-form). The former is rarely found in the field. The occurrence of the M-form was studied under the various rearing densities in the Petri dish (12 cm in diameter, 7 cm high). The result is that the occurrence percentage of the M-form is the lowest when insects are reared solitarily and increases with the increase of the density to the maximum effect and then decreases as the density increases further. Judging from the fact that when the present cricket is reared being isolated by a wire-gauze in the various rearing spaces respectively corresponding to ones in the experiment above, the occurrence percentage of the M-form is always low showing the values similar to the solitary rearing of the above experiment, the occurrence of the M-form seems to be related to the direct contact among insects. As the cutting of the antennae makes all the crickets develop to the B-form in the group culture, it seems that the antennae plays an important role in the density effect and the lowering of the occurrence percentage of the M-form as the high density is related to the wound induced by the living under the high density.

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The writers wish to dedicate the present dissertation to Dr. Kinji IMANISHI, who takes interest in our study and has given many suggestions. The relative egg sixes of various species of bees were compared with relation to their modes of life. There are two distinct specializations in egg size, dwarfism and gigantism. Dwarfism is seen in parasitic and social species, while gigantism occurs in subsocial species, especilly of the subfamily Xylocopinae. The biological significance of these specializations is discussed. In connection with this, the number of ovarioles was compared among diverse groups of the Hymenoptera Increased egg production is achieved in the Hymenoptera in two different ways : multiplication of ovarioles or increase of efficiency of each ovariole.

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The mode of life of the Long-tailed Tits (Aegithalos caudatus) is discussed bored upon the seasonal fluctuations of the population sizes, range of distribution, and conditions, of dispersion and flocking. The observations were made during 1957-1960 in the area of 1.2 square km along of the River Tenryu, Nagano, and the results were published already. The mode of life may consist of five phases ; winter stability, spring instability, spring stability, summer congregation and autumn instability phases. On the area studied, the Long-tailed Tits are the constant residents and the teritories of its pairs are in the winter home ranges. So that, the winter flocks extend to the peripheral parts of their habitat, and this winter stability phase might have influence on the breeding population and breeding sites. It is observed that the family flocks crowd into the central parts of their habitat during the summer congregation phase. Comparing with other tits of the Paridae, the peculiarities of the Longtailed Tit are found in the summer congregation and the change from the winter stability to the spring stability. It seemed that such phenomena are more similar to gregarious birds of other families rather than to the other species of the Paridae, but the summer large crowding is broken up by the winter flocks during autumn. This mode of life must be compared with the other local populations of the Long-tailed Tits and more other species.

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The intertidal zonation of the marine algae along the coast of Kamisaki Bay, a small inlet in the Sea of Kumano, was studied. The field work was carried out in the winter of 1965. As the results of the investigations, two communities were found. The Hizikia fusiforme-Eisenia bicyclis association was found at the exposed shore of the bay, and the Monostroma nitidum-Scytosiphon lomentarius association at the sheltered shore. The important factors with regard to the distribution of the algal communities are the size of the bay and the wave action.

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The smoke of γ-BHC was used to estimate the density and the biomass of forest arthropods. The problem of determining the number of quadrats is considered in this paper. A six meter by six meter quadrat consisting of 36 units of 1 m^2 vinyl sheets was set up in a beech stand of the Ashu Experimental Forest of Kyoto University in Kyoto Prefecture in May and July of 1965. On one calm morning five containers of γ-BHC were made to smoke. The arthropods fell and died on the sheets and were collected. The minimum unit area and its size were calculated by the application of the statistical theory to estimate the density and the biomass of the arthropods. As for the density, if 20 units of 1 m^2 were used, the values 20 per cent of fiducial limits to the average on 95 per cent confidence can be obtained. The variance in the biomass, however, was somewhat larger than that in the density, so a larger area is required to get the values of the above mentioned. It was estimated to be 30-50 m^2.

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The vertical distribution of freshwater planarians in the Mt. Teshio district in the Kitami Mountains and in the Okhotsk seaboard district in North Hokkaido is reported. The highest peak, Mt. Teshio-dake (1557.6 metres above sea level), is situated at the southern corner of the Kitami Mountains (Lat. 43°57′N. and Long. 142°56′E.). The Okhotsk seaboard district is the flat-surfaced hilly land. The main river systems of the area surveyed are the Teshio, the Ishikari and the Shokotsu. The Shokotsu River discharges into the Okhotsk Sea ; the other two rivers empty into the Sea of Japan. Surveys were made in the summers of 1963,1964 and 1965. In the area surveyed, six species of freshwater planarians, Phagocata vivida (IJIMA et KABURAKI), Polycelis sapporo (IJIMA et KABURAKI), Polycelis akkeshi ICHIKAWA et KAWAKATSU, Polycelis auriculata IJIMA et KABURAKI, Polycelis schmidti (ZABUSOV) and Dendrocoelopsis lacteus ICHIKAWA et OKUGAWA, were found. Ph. vivida and Pol. auriculata were common in the localities in the Rubeshibe River, one of the tributaries of the upper part of the Ishikari River. Ph. vivida was also collected in some localities in the upper part of the Teshio River. Pol. auriculata was also collected in some localities in the upper parts of the Teshio River and the Shokotsu River. Pol. schmidti was collected in the cold-water streams in the upper parts of the Teshio River and the Shokotsu River and in some springs in the Okhotsk seaboard district. Pol. sapporo was most common in the localities of the seashore and mountainous districts. Pol. akkeshi was collected in some localities in the Mt. Teshio district. Pol. akkeshi was, however, the most dominant species in the Okhotsk seaboard district. Den. lacteus was collected only in the localities in the Okhotsk seaboard district. The altitude range of the distribution and inhabitable water temperature range of the above-mentioned species which were found in the Mt. Teshio and the Okhotsk seaboard districts are as follows : Ph. vivida (alt. 280-840 m, 6.3-12.5℃) ; Pol. sapporo (alt. 1-1000 m, 7.9-18.2℃ ; including the data of Pol. akkeshi) ; Pol. auriculata (alt. 280-1000 m, 6.3-12.5℃) ; Pol. schmidti (alt. 4-840 m, 4.8-11.8℃) ; Den. lacteus (alt. 1-90 m, 10.5-14.5℃). The type of vertical distribution in the area surveyed is SVA-VA (the Ishikari River) or S-SVAC (the Teshio River) or SC-SAC (the Shokotsu River and the Okhotsk seaboard districts).

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Observing the mode of spatial distribution of the plants in the plant communities in the fallows of the Tokyo Agriculture Experiment Station and the dune of Chikura Machi, Chiba Prefecture by means of the quadrats which are placed in a row in the region S_j (j=1,2,......, m) in Fig. 1 and by splitting each quadrat into a number of smaller quadrats, the present author found that (1) the mode of spatial distribution of the plants is shown by the expressions : [numerical formula] and that (2) the frequency distribution of the number of the plants in a smaller quadrat in the jth quadrat is shown by the Poisson distribution : [numerical formula] derived theoretically from stochastic processes, where N is the number of plants in the jth quadrat, d is the distance between the first quadrat and the jth quadrat, P_j (γ) is the probability of the appearence of γ plants in a smaller quadrat in the jth quadrat, and N_0,A, α, and μ_j are constants.

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