The formation of the second ring-spot sometimes takes place in the present stage (Fig. 42).
On the first segment only there is210 no spot, and here no ring-spot is afterwards formed.
At a later period these two222 crescents and also the two primary nuclei coalesce, producing a ring-spot which, as in Fig. 61, Pl.
In this way the first ring-spot probably arose in some species on only one—the penultimate segment.