STUDIES of development and reproduction in marine invertebrates are usually limited to the natural breeding seasons of the animals concerned. In order to overcome this time restriction with regard to Aplysia punctata (Gastropoda, Opisthobranchia), and in the hope of establishing a method which might be applicable to other animals, we tried to induce early spawning in Aplysia collected from a sublittoral population in Treaddur Bay, Anglesey. These collections were made in early February 1965, when the field sea temperature was 6.7° C. The natural breeding period for this species of Aplysia lasts from early May, when the sea temperature is about 9° C, until October, when it is about 14° C (ref. 1).