The writer has studied since August 1961 on the promotion in spawning of commercial abalone of Japan,
Haliotis diversicolor supertexta LISCHKE by the stimulation of fluctuations, high and low, in the temperature of water. He succeeded in getting fertilized eggs of this species in July 1963 and observed their development for 201 days after fertilization.
The results so far obtained are summarized as follows:
1. Spawning behaviors of this abalone are peculiar. Spawning is made near water surface. Female touches the wall of aquarium by the posterior end of her pedal sole, its anterior part being separated from the wall, and then the shell is lifted and the muscle contracted rapidly, so that eggs are emitted in the water through from third to sixth respiratory pores of the shell.
2. The genital products of both sexes are set free in the water through respiratory pores. Soon the eggs sink down to the bottom.
3. Fertilization takes place in the water after eggs and sperm have been emitted.
4. The eggs are spherical. Their size is 0.20mm in diameter including egg membrane, and their yolk is 0.16mm in fertilized condition (Plate I1).
5. The division of the egg is total, unequal and spiral (Plate I 2-6).
6. At the temperature of 26.2-26.8°C, the trochophore escapes from egg membrane within 6 hours after fertilization. The trochophore has apical cilia on top (Plate I 7).
7. The trochophore is transformed into the veliger stage within 10-11 hours after fertilization (Plate I 8, 9).
8. The veliger which finishes torsion shows the origin of cephalic tentacles, eyes, foot and operculum. Larval shell is 0.25mm long (Plate II 1).
9. The veliger settles to the bottom within 43-46 hours after fertilization (Plate II 2).
10. The first ciliary lobe appears in 3.5 days after fertilization and second one appears in 13 days after fertilization, at this time the shell being 0.23mm long (Plate II 3, 4).
11. The first respiratory pore forms in about 23 days after fertilization, at this time the shell being 1.8-1.9mm long (Plate III 1, 2).
12. The shell becomes 2.38cm long on the 201st day (Fig. 4).
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