Mode of Cleavage of the Eggs of Hydroides norvegica in the Mediterranean

Abstract

IN a recent paper¹, it was pointed out that the eggs of the marine polychaete Hydroides norvegica may have different cleavage patterns in the North Sea and in the Mediterranean. Whereas at the Kristineberg Zoological Station (near Fiskebäckskil), on the west coast of Sweden, Wolsky found the early cleavage to be spiral and equal, an earlier observer, Soulier², working at Cette (Séte), on the Mediterranean coast of France, found it orthoradial and unequal. It was suggested that this difference may be a sign of differentiation of two distinct physiological races within the species, and it was thought desirable to check the correctness of this suggestion. A short visit to Naples in April 1954 and the hospitality of the Stazione Zoologica, for which I am greatly indebted, made it possible to carry out such a check on Mediterranean material.