卵胎生淡水産腹足類カワニナの胚培養法と発生の概要

抄録

Embryos of an ovoviviparous freshwater snail, Semisulcospira libertina, were removed from the brood pouch in order to observe embryogenesis in various artificial solutions. For the embryo culture at the constant water temperature of 25℃, Chernin's Basic Salt Solution (BSS) was better than physiological salines used for culturing the tissue of this snail. However, embryogenesis was not observed in distilled water or in the habitat water. Antibiotics were added to the culture solution to prevent contamination and the culture solution was renewed every day. The first two divisions are equal. The polar lobes can be recognized at the first, second and third cleavages. Meiotic division is probably completed in the brood pouch. The third and forth are unequal and dexiotropic. As embryo of this snail is yolk-rich, detailed cleavage after the forth division could not be observed. Following the morula and the blastula stages, the gastrula with a large blastopore can be observed. The trochophore has a prototroch, and the rudiments of the head, visceral mass and foot. After the trochophore stage, the blastopore becomes the rudiment of the mouth. Torsion occurs as a result of pronounced enlargement of the visceral mass at the pre-veliger stage. The differentiation of the digestive system is delayed because of the large quantity of yolk. It took 17.2 days at 25℃ for the fertilized egg to develop into the veliger, exhibiting cardial pulse. Some 88 percent of the embryos underwent normal development.