日本産普通多足類の後胚発生XIII : ヒラタヤスデの生活史(3)

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The moulting process of Bazillozonium nodulosum was observed under laboratory conditions. The species never constructs a moulting chamber or bell. Instead, the process can be divided into four periods : the pre-rigidation period, the rigidation period, the intermediate period and the recovery period. During the pre-rigidation period, the animals are under active, their bodies swell slightly owing to internal pressure, and the anal segment protrudes (Figs. 2 and 3). During the rigidation period, they lie spirally curled under rotten wood, small rocks, etc. (Figs. 4-7). During the intermediate period, the actual shedding of their old skeleton takes place ; this serial process is shown in figures 8 to 13. New somites are soft and pale red in colour. The recovery period that follows is not as clear as that of other groups of Diplopods described by several other authors. After shedding the animals begin to be active, always leave their exvia one's place (Fig. 14). However, under active, their new exoskeletons become gradually hard and coloured. During this period, new somites can be distinguished from the old somites by their keel size or by whether the defense glands have granules or not (Figs. 15 and 16). In old larvae and adults the four periods of the moult need three to four weeks as follows : the pre-rigidation is about one week, the rigidation period four to eight days, the intermediate period a few hours, and the recovery period one to two weeks. 2) According to observations made both in the laboratory and in natural habitats, the moult is found to occur intensively in eary summer (beginning of May through June) and early autumn (beginning of September through mid October) and individuals in various developmental status are found during both periods. 3) The moult of about 400 individuals was observed, and the increase of body segments after each moult was studied. The results are shown in table 1. The body segments vary from 2-8 segments, but occurs as 4-7 segments in 90% of the cases. It is accordingly conceivable that this variation produces a seriated number of body segments found in the species. The data were analyzed for mutual relations as given in figure 1. It will be inferred from this figure that the anamorphosis of this species has six or seven larval stadia and the adult followed them. 4) The numerical relation of legs to body segments in 1754 individuals were investigated. There was a wide variation as summarized in table 2. Thus, the anamorphic stadia of this species can be assumed from the investigation of the moult. The number of body segments and pairs of legs in each stadium are presented in table 3.
社団法人日本動物学会の論文
1963-02-15

日本産普通多足類の後胚発生XIII : ヒラタヤスデの生活史(3)

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