Before the Ise-wan Typhoon (September 1959), the Yoshino River (Nara Prefecture) had a very large standing crop of benthos. However, the benthic communities were destroyed considerably by the Typhoon. This river was studied in 1960,1964〜1967 (all during August), after the Typhoon, and the results were discussed and compared with the data of TSUDA and GOSE (1953,1954) and TSUDA and KOMATSU (1960). The conclusions are summarized as follows : After the benthic community was destroyed by the flood, it recovered gradually. The diversity of species tends to increase with the lapse of time. Dominant species also changed with time and the standing crop increased. The net-spinner's coefficient and Stenopsychidae coefficient increased. The rate of the increase of the standing crop was higher at the upper reaches than at the lower reaches. The curve of the increase of the standing crop with the lapse of time is shown as a sigmoid curve (Fig. 10).
Whether the annual fluctuation of the yearling population of Gnathopogon caerulescens in winter is influenced by the fluctuation of growth of the under-yearlings was examined. Specimens for examining the size distribution of the under-yearlings were sampled from the fishermen's catches with a trawl net and trap from 1962 to 1967. The fishing was carried out by trawling in winter, and by trapping during the spawning season. The mean body length in early winter fluctuated annually from 5.75cm (1962 year class) to 6.59cm (1964 year class) and the coefficient of deviation fluctuated from 0.136 (1966 year class) to 0.156 (1962 year class). These results suggest that there is considerable annual fluctuation in the growth of the under-yearlings. Poorly grown individuals, smaller than approximately 6cm in body length, died between late winter and early spring every year (Fig. 1). This phenomenon reflects that the mean body length in early spring from 6.65cm (1965 year class) to 7.61cm (1964 year class) was greater than those in early winter and the coefficient of deviation from 0.075 (1964 year class) to 0.124 (1966 year class) was less than those in early winter. The survival rate in each year class in early spring was estimated by comparing the body length distribution of the under-yearlings in winter with those in early spring (the estimation method is shown in Fig. 3). These values fluctuate annually from 35.7 (1966 year class) to 57.0 (1965 year class) per cent. This fluctuation of survival rate seemed to be caused partly by the yearly differences of the growth rate up to the early winter and partly by the size specific survival rate. The index of number of the estimated survivors in early spring was computed by dividing the index of the biomass by the mean body weight of the under-yearling fish in winter and multiplying by the estimated survival rate. The index values of the estimated survivors and the actual ones showed almost parallel annual fluctuation. The correlation coefficient between the two index values was 0.882.
1. Lakeside people say that Lake Suwa has recently become badly polluted. To prove this limnologically some observations were made three times in 1966 concerning the turbidity and the amounts of suspended and dissolved matters. The results were compared with those obtained in the past. 2. The waters in the littoral region of urban areas become so heavily stained with the rapid growth of population and by the extension of industrialization that the values of transparency by Secchi's disc are even less than 50cm. The values in the pelagic zone, however, have decreased but very slightly during the course from 1904 to 1966. 3. The dissolved matters together with the colloidal ones in the lake are exceedingly larger in total amount than that of the suspended solids occupying about 80〜90 percent of the total residue on evaporation. They only show slight increase in the course of years in the pelagic waters, while in the littoral regions there is a surplus of substances in solution accruing from the towns. 4. The suspended solids are composed mainly of organic constituents occupying about 60-80 percent of the total weight. They are at present about five to 15 times as much as those in the years before 1950 either in total amount or in the amount of organic ingredients. 5. The lake water becomes almost colorless and transparent by filtration through any filtering material. So the recent striking pollution in the eyes of the people is no doubt principally due to the marked increase of substances in suspension. 6. Among the suspended solids, the most important factor that makes the water opaque to light is cnsidered to be the prosperous occurence of plankton organisms. The results of analysis show that the contents of nitrogen and phosphorus in the lake water have recently increased very much with years as the essential nutrients for plant organisms. This is caused by the increased discharge of municipal wastes and by the yearly accumulation of organic constituents generated from decomposition of dead bodies of plankton and hydrophytes. 7. In addition to the above the remarkable floating of bottom sediments on windy days is also responsible for the turbidity of the lake. In recent years the lake has become shallow and the bottom oozy by the continual addition of decaying materials.
This paper presents the allometric relation of the body weight to the body size of the workers of Formica japonica MOTSCHULSKY in various seasons, and an allometric analysis of their fluctuation of corpulency. Even though there was weak correlation between body weight and head width in summer, two rows of the mode on the correlation diagram were found, being expressed by the formula Y=aX^3 where Y is the live or dry weight, X is the head width and a is the index of corpulency. The row shown by the corpulent type individuals of the workers was seen in all seasons, but that shown by the lean type was not seen in the hibernating colonies. The worker working on the ground in winter showed the row of the lean type. As'a'in the formula is independent of the body size, the body weight can be divided into two component items, the one representing the weight depending on the body size and the other representing the factor depending on the corpulency. The ratio of dry weight to live weight of the ant body is also independent of the body size. This ratio in the summer workers is smaller than that in the hibernating ones ; the difference being about 10%.
From field observations and laboratory experiments, it was estimated that the fecundity and the survival rate of the smaller brown planthopper, Laodelphax striatellus FALLEN, may be remarkably higher in the early seasonal and the earlier cultures of rice plants in comparison with those in the common spring habitats, such as weed lands, grass, wheat and barley fields, because the former was more suitable as food to the planthopper and accompanied with a lower level density of Araneid spiders preferably attacking the planthopper. Thus, the early seasonal and the earlier cultures of rice plants seem to provide a habitat
Three wing-forms were seen in the cricket, Gryllodes sigillatus WALKER, when the larvae were reared under different densities and temperatures. Almost all individuals reared solitarily became the micropterous form and the ones reared in groups the micropterous or macropterous forms in both sexes. A few incidences of the median form was seen in female. The incidence of macropterous form increased as the larval density increased and temperature rose. It was suggested from the experiment in which the larval density was changed at the sixth instar that the wing-form is determined mainly by the fifth instar. The difference in body size and shape among the wing-forms was discussed based upon the principal component analysis on six characters (five measurements of body parts and body weight). It was shown that the length of the pronotum was shorter in the macropterous than in the micropterous and median forms. The body size became smaller as the larval density increased, and varied in relation with the rearing density. The body size of the female micropterous form is more strongly influenced by the density than the macropterous form : The body size of the female micropterous obtained from five larvae rearing was greater than that of the macropterous form obtained under the same condition, but that of the micropterous form obtained from ten larvae rearing was smaller than that of the macropterous form. The body size seemed to be influenced mainly in old larval stage. It is, therefore, suggested that the incidence of the wing-form and body size, both of which are affected by the larval density, are independent to each other. The days of larval development and the fecundity were not different significantly among the wing-forms. The shape of the oviposion curve shows that the maturity of the ovary in the adult is faster in the micropterous than in the macropterous and median forms. It is concluded from the facts mentioned above that the wing-form in G. sigillatus is a phenomenon similar to the phase in locusts and other insects.
Experiments were done to analyse the process generating spatial distribution pattern of the eggs laid by two species of bean ■evils, C. chinensis L., and C. rhodesianus Pic. (species name of the latter is not yet determined by taxonomist). The experiments were conducted under the the condition of 30℃ 75% R. H. and 16hr. illumination. The cage used for the experiment was 64×64cm in size and less than 1cm in height. In the cage 64 beans were scattered evenly or in clumps, (Fig. 1). ■ chinensis, the value of I_δ. an index showing the spacial distribution pattern of the eggs, the number of eggs oviposited, and the number of eggs per bean increased with the increase of the number of females released. In C. rhodesianus, too, the number of eggs deposited and the number of oviposited beans increased. In this species, however, the I_δvalue and the number of eggs per bean remained unchanged with the increase of number of females released (Table 1). In C. chinensis, the number of oviposited beans changed with the variation in bean distribution. In. C. rhodesianus, the number of eggs per bean and the value of I_δ changed. How ver, in C. chinensis, the number of eggs per bean and the value of I_δ did not change with the variation in bean distribution. In C. rhodesianus, the number of oviposited beans remained unchanged. In both species, the number of eggs oviposited showed no significant difference statistically with the variation in bean distribution though in C. chinensis, the averages were 76.7 in uniform distribution and 52.8 in clumped distribution (Table 2). In C. chinensis, and adult female had a strong tendency to avoid the beans already oviposited and to look for fresh beans for her oviposition, this bringing about the oviposition of a rather uniform distribution of eggs over the area. C. rhodesianus female was less discriminative and her eggs were laid randomly on beans within a limited area so that the eggs tended to be distributed in clumped pattern. It was observed that the female of C. chinensis walked round a bean in a large circle