セタシジミの生態學的研究-I : 成長に就いて
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概要
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ORTON and ISAHAYA set forth that bivalves make a concentric circular resting zone on the surface of shell as a sign of their growth. In order to know the time in which the resting zone is formed and the rate of growth of the animal in question, the author has measured the distance between the umbo and each resting zone as shown in the table 1 (h1-h7). The results drawn from the present scrutiny are as follows. The resting zone appers to be formed twice in a year irrespective of size of the shell. One is formed in June, and the other one dring the season from December to February. The shells reach to a length ef 9mm in height in the first year, 17, 22, 25mm in the subsquent years.