フサクロムシPeltogasterella socialis Krugerの初期発生

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1) When the eggs contained in the ovary begin the first maturation division, they are extruded into the maternal mantle cavity. The whole of the embryonic development up to the nauplius stage proceeds in the mantle cavity. 2) In about 2 hours after the extrusion of the egg into the mantle cavity, the first polar body is expelled out of the egg and the second maturation spindle appears. By this time the entrance of spermatozoon into the egg takes place. The conjugation of pronulei occurs about 2 to 3 hours afterwards. 3) The first and the second cleavages are holoblastic and four blastomeres of equal size formed. The subsequent cleavages, however, do not affect the yolk and blastomeres at the animal pole go on rapidly dividing in all directions so as to form a continuous blastoderm over the egg. Soon after the blastoderm is complete, an invagination occurs at the vegetal pole. The invaginated cells, however, do not form a complete endoderm and disperse in yolk ; finally they disintegrate. After this, three pairs of protuberances appear in the blastoderm ; they are rudiments of the appendages of the nauplius. In later stage, an eye-spot, a nervous ganglion, and muscles which move the appendages appear in the cephalic region, and some large cells with conspicuous nucleoli in the thoracic region. 4) Hatching of the nauplius larvae takes place in about two weeks after the extrusion of the eggs into the mantle cavity. The larvae are expelled from the mantle cavity through the mantle opening by the rythmic contractions of muscular mantle. The nauplii are actively heliotropic and swim about in sea water. After four successive moults in four days the nauplii transform into the cypris larvae.
社団法人日本動物学会の論文
1957-06-15

フサクロムシPeltogasterella socialis Krugerの初期発生

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