1977年7月から1979年8月までに三重県鳥羽市今浦の潮間帯で連続採集法と標識法によってアマガイの成長および年齢の解析を行った。雌雄とも成熟期の試料において殻長10∿11mmのところで殻長に対する殻巾の相対成長の変曲点を示すが, 雌雄には成長の差異がなかった。また, 成熟した雌にみられるcrystal sacは殻長10mm以上の個体に限られ, 本種の性的成熟は, 成長曲線から検討して満2年を迎える年齢群以上のものと考えられる。個体群は満0歳, 1歳, 2歳の3群から構成されており, 5∿7月頃に産卵されたものは8月には殻長2∿3mmの幼貝に成長し底生生活を始めるようになる。1年後には9mm, 2年後には14mmに成長し, その後満2年を経た個体はほとんど成長することなく秋に死亡するものと翌年の産卵期に死亡するものとに分かれ, ほとんどが満3年未満で死亡することが明らかになった。

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In order to clarify the role of amoebocytes in the midgut of the hard clam, Meretrix petechialis, the behavior of these cells and changes of pH value were investigated after feeding granules of different sizes such as yeast, potato starch, rice powder, kaolin or diatom earth. After being immersed in seawater suspended with those materials for 24 hours, the midgut of the hard clam was cut open. The total number of amoebocytes in the midgut were counted with THOMA's hemocytometer after staining with LOFFLER's methylene blue. The pH value was determined with the test paper (BTB or MR). Changes in total number (AT) and relative frequency (R) of amoebocytes, which was indicated by the ratio of AT in fed group to AT in control group, as well as pH value in each fed group are summarized as follows. AT or R varied with the size of the materials supplied, i.e., R was 80-160 when the particle size was 3-70 μm, and R ascended over 200 when the size exceeded 130 μm. No difference in AT or R was found between the groups supplied with organic materials and those supplied with inorganic ones. There was no relationship between AT and pH value in any group.

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Egg cases, eggs and hatched larvae of Cypraea vitellus were observed. Egg cases over which the mother lies for protection are pyriform measuring 2.5×1.5 mm and contain some 600 eggs each. Swimming veligers were escaped from egg cases on the 12th day since they were laid. Veligers measure 190 μm in shell length, with bilobed velum. Emptied egg cases were eaten by the mother shell.

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In this paper, four Japanese species of the genus Nipponochloritis (Camaenidae) are discussed in view point of morphology of the shell and genitalia.

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