As part of a series of studies on the function and morphology of skeletal muscles, I investigated histologically the muscle fiber type of the tibialis anterior muscle of lorises which show slow behavior and galagos which show quick behavior, both of which are prosimians, in order to analyze the composition of muscle fiber types of the skeletal muscle from the viewpoint of the locomotion system. The red muscle fiber diameter was the largest, followed in order by that of the intermediate muscle fiber and white muscle fiber in the loris. The frequency of red muscle fiber was the highest, suggesting that the M. tibialis anterior of the loris is the red muscle type with slow contraction. In galagos, by contrast, the red muscle fiber diameter was small, and the diameter of the both intermediate and white muscle fibers was large. The frequency of red muscle fibers was markedly low in galagos, resulting in the prepondence of muscle fibers being white and intermediate muscle fibers. The M. tibialis anterior of galagos thus shows white muscle type or intermediate muscle type, which is fast contraction. Although both loris and galagos belong to the Lorisoidae, there was much difference in the frequency of muscle fiber type between them. Composition of muscle fiber type of these prosimians is the relationship between muscle fiber types and their diameters. These results suggest that the functional difference in behavioral pattern in loris and galagos is reflected by the composition of muscle fiber type.

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We surveyed chimpanzees in the Nimba Reserve, which is located 10km away from Bossou and have not been studied much until now. Only one encounter and a small number of field signs were recorded. The chimpanzees are appeared to be very timid against humans. Their population density is thought to be low mainly because the hunting pressure by human is high, Regarding tool-using behavior, there were some interesting findings. Instead of oil-palm nuts of Bossou, a few other nuts were found cracked and are supposed to have been eaten by the chimpanzees. There seems to be cultural difference in tool use between Bossou and the Nimba Reserve.

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We observed a low birth weight chimpanzee (Pan troglodytes) infant (birth weight 790g) and compared the results with observations of other nursery chimpanzees and with those of wild chimpanzee infants in order to establish what basic behavior is, in spite of differences in environment and birth weight. There seem to be three kinds of behavior; (1) that which occurred in the very early period after birth despite differences in birth weight, (2) that which occurred after weight reached the average standard (about 1800g, Graham 1970, Gavan 1952), (3) that which differed according to environment.

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