traced to its adult form; and we have the converse of the case of entoconcha where the true affinities of a greatly modified adult are shown by its younger stages.
I give four figures to illustrate one such instance, which is not by any means exceptional or extreme; and in certain groups of animals, such as the Crustacea, such cases are quite numerous.
Fig. 5 is a magnified side-view of a crustacean, Sergestes, which is not quite full grown, but still essentially like the adult; and Fig. 6
Fig. 7.
is a similar view of a closely related form, Lucifer, in a similar stage of development. Their close relationship is obvious at a glance, and their resemblances, which are much more conspicuous than their differences, are rendered more obvious by careful study; but the case is
