ABSTRACT Several experiments done in our laboratory make it likely that in the egg of Limnaea stagnalis there is a cortical morphogenetic field (Raven, 1949, 1952, 1966). One of us (Raven, 1963,1964,1967) has studied the origin of this morphogenetic field. In the newly laid egg cell there is a vegetative pole plasm, occupying a sector of about 110 degrees with its apex near the centre of the egg. It is situated somewhat obliquely with respect to the longitudinal axis of the first maturation spindle. Moreover, a circle of six lenticular subcortical patches of cytoplasm are found in the equatorial region of the egg. These ‘subcortical accumulations’ (SCA) are arranged according to a regular pattern. Four of them are situated close together on one side, occupying about 180 degrees of the egg circumference; two somewhat larger SCA lie on the opposite side. The SCA, together with the obliquity of the vegetative pole plasm, define a pattern which is polar, dorsoventral and nearly symmetric, though a slight asymmetry seems to be present.