Abstract
Number of swimming larvae and attached spats which are collected by nets and collectors respectively fluctuate with year (Fig. 1). It is conceivable that the changs in appearance of the larvae and spats run parallel with the fluctuation of spawning of the shell. The scallop is induced to spawn by rising in temperature in the laboratory and the low effective temperature of the spawing is 8.0-8.5°C. and the shell is stimulated by only sudden rising above the effective temperature even by 0.5°C. The stimulation for induction of spawning is more effctive in high breeding season, viz. April, and ovarial eggs degenerate with the beginning of May.
Basing upon above facts and curves of coast temperature (Fig. 2), the spawning of the scallop in Mutsu Bay is perhaps induced by the sudden rising of water temperature affected by the violent warm current flowed into the bay during the breeding season.
