The diurnal rhythm of the vertical migration of fish has been noticed as a factor affecting the efficiency of fish catching. The Yellow croaker, the most important demersal fish in the East China Sea and the Yellow Sea, is a representative species that migrates vertically with certain rhythm. The diurnal vertical migration of this species was therefore investigated by analyzing the catch in conjunction with the time of day reported from trawlers operating in these waters. The seasonal change of the diurnal rhythm and the influence of the population size on this behavior were also examined (Fig. 1). The vertical migration of this species, a zooplankton feeder, seemed to be affected by the feeding behavior. The fish descends to the sea bottom in the daytime and ascends toward the surface at night in company with the upward movement of the diurnal vertical migration of such zooplankton as euphausiids, copepods and other crustaceans. The hourly change of the mean catch per hour tow (Table 1,Fig. 2) indicated that the values were generally large during the daytime with a peak around noon. This was particularly clear durnig the feeding period, October and November, while it was not distinct during the wintering period, January and February, The pattern of the feeding period, was found more clearly in the monthly change of the day-night ratio of the mean catch per hour tow (Fig. 5). The day-night ratio of the mean catch per hour tow for each size category (Table 3) or for growth (Fig. 4) revealed that the diurnal movement became more pronounced with the development of the fish, although no remarkable difference in size was observed during either the wintering or the feeding periods. The strength of the diurnal periodicity differed with the locality of the fishing grounds, i. e. the diurnal rhythm of the yellow croaker inhabiting the Yellow Sea was much stronger than that of the southern stock living in the East China Sea (Table 4,Fig. 5). The relation between the yearly change of the population size index and that of the day-night ratio (Fig. 6) afforded a negative correlation, which presumably suggests that the diurnal rhythm is not distinct when the population size is small and vice versa.
Observations on the mating behaviour of two species of the bean weevils, Callosobruchus chinensis and C. rhodesianus (?) were done under the conditions of 30℃, 75% R.H. and daily photophases of 16 hrs. When a female and a male of C. chinensis were introduced into the experimental arena, the male first moved around rather sluggishly, but suddenly he begun to move quickly with rapid movement of his antennae. Such change of behaviour, called 'activation' here, could not be seen when a male alone was introduced into the arena. Once the male found the female, he continued to follow her very closely, and struck her with his antennae. During copulation, the female remained stationary and exhibited no excitement. The male of C. rhodesianus walked around more actively than C. chinensis, and no change of his behaviour was observed in the course of finding the female. Before copulation, the male stood near the female and rapidly struck her with his antennae. During this duration, the female remained quiet. Sometimes mutual sparring with the antennae between both sexes was observed in the first step of mating behaviour. The male did not show the behaviour of running after the female. Homosexual behaviour, e.g. pursuing a male by another male, did occur frequently in C. chinensis but not in C. rhodesianus. In both species, a male found a female more easily when the female had been introduced in the dish 10 minutes prior to his entrance, than when she had been introduced at the same time. They could mate in darkness as well. When the male's antennae were amputated, he could not find a female. The female mated previously lost her attractiveness to the male. Reaction of the male to the female is specific for each species. In C. chinensis, the time required from the introduction of the male to his 'activation' as well as to his success of mating with the female was shortened as the size of the arena was reduced. While, in C. rhodesianus, the shortening of the time to mate was not so great as in the former. Even in a small tube, the males whose antennae were amputated could not mate in C. chinensis but some of them could mate in C. rhodesianus. These and other observations suggest that some stimulus (or stimuli) perceived by the male through his antennae, which may probably be olfactory in nature, is important in C. chinensis for the male's attraction to the female. In C. rhodesianus, the discovery of and copulation with the female by the male seems to depend to a greater extent upon the encounter by chance between the male and the female. Pre-mating period was very short in both species. The effect of delayed mating on the number of eggs laid per female was less marked in C. chinensis than in C. rhodesianus. When a female mated only once, the percentage of unhatched eggs was higher in C. rhodesianus than in C. chinensis.
The modes of netting of web spiders each of which comprises three components (occupation of space, netting process and web-form) are divided into the following five types : (1) vertical orb-web type, (2) horizontal orb-web type, (3) cubic web type, (4) sheet web type, and (5) fixing web type. To occupy the scaffolding stand and space for netting, some competitive or cooperative relationships are found between the individuals having the same of different mode of netting, and through these coactions each web spider community in each habitat is organized. Eleven different community types, each corresponding to the difference of habitat (conditions and localities), are found. The correspondent habitats and community types are as follows : [table] Among these Ara, Ara', L, N, Arg, Tr, Th, U' types are considered to form a set of community types in a district and are named as "the community lump A", while N', L, Arg', Tr, Th, U types form another set, and is called "the community lump B." The communities belonging to lump A are distributed over Fastern Siberia, Sikhote Alin, Northern and Eastevn Hokkaido, Honshu, Sikoku, Kyushu, Yakulsle, Tanegashimalsle, etc, and the distribution areas of those belonging to lump B are Takaralsle, Kikailsle, Amamilsle, Tokunoshimalsle, Okierabulsle, Ooronlsle, Okinawalsle, Ishigakilsle, Iriomote Isle, stc.