Each egg is surrounded by an inner membrane and an outer capsule which swells as development proceeds. The number of eggs in each mass is large, varying between 1000 and 1200. Cleavage is total, equal and of a typical spiral nature. Information concerning the nature of gastrulation is apparently not available. By the fifteenth day, the larvae are showing lively movements, and by the seventeenth day, the shell anlage appears.
Hatching occurs on the twenty-sixth day.
The mouth is open. The velum has long cilia, and is marked by a brownish-red border. Beobachtungen und Versuche an den Eiern von Littorina und Lacuna. Meere, N. F., Abt. Laich und Jugendformen von Littorina und Lacuna.