ABSTRACT
THE MOMENT of fertilisation is the conventional point of origin from which to date the existence of a new individual. We have seen in the last chapter that in fact many processes which are most important for the developing embryo occur before fertilisation, during the maturation of the egg. It cannot be denied, however, that fertilisation is, normally at least, the most crucial event within the continuous series of changes by which the new creature comes into being. It is not a simple occurrence, at which there is only one happening of importance; but its two important phases succeed one another quite quickly, and although they can be dissociated from one another in experiments, they are normally closely bound up with each other, so that fertilisation appears as a single, though complex, event (Fig. 3.1).
