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Abstract: The presence of photoreceptor cells in the spinal cord of amphioxus hasalways been known by the neuroanatomists, but the information about thereaction to photo-stimulus of the animal is rare. Last summer we carried outan experiment in Qingdao in the purpose of examining the sensitivity of theamphioxus (Branchiostoma belchari) to monochrome lights of different wave-lengths. Over two hundreds of B. belcharis were tested individually byprojecting monochrome light directly on them when they were resting at thebottom of a small plexiglass aquarium. The results showed that B. belcharis seem to be highly sensitive to themiddle band (534-577mμ) of the visible spectrum, i. e., green and yellow,less sensitive to blue and orange (459mμ, 602mμ), and almost insensitive ?ored (635mμ). At the end of the experiment we made an observation on the color lightpreference of the amphioxus. In each trial 10 belcharis were put in theaquarium, which was then illuminated with red light on one side and withanother light, such as white, blue, green or yellow on the other side. Theuneven distribution of the animals in the two halves of the aquarium wassimply due to the fact that when the lights were on, the animals inthe more-effective area moved vigorously and came into the range of theless-effective area incidentally while the animals in the less-effective arearemained motionless, so the numbers of the animals in this area increased. Here we use the term photo-kinetic reaction so that it is distinguishedfrom any other kind of taxis.

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