Elizabeth Cary Agassiz, Louis Agassiz: his life and correspondence, third edition

For the last few days I have been especially occupied with the development of the medusae. In studying the actini$e I have made a striking discovery, and I should be glad if you would communicate it to the Academy in advance of the illustrated paper on the same subject, which I hope soon to send you. Notwithstanding their star-like appearance, the star-fishes have, like the sea-urchins, indications by no means doubtful, of a symmetrical disposition of their organs in pairs, and an anterior and posterior extremity easily recognized by the special form of their oral opening. I have now satisfied myself that the madrepores have something analogous to this in the arrangement of their partitions, so that I am tempted to believe that this tendency to a symmetrical arrangement of parts in pairs, is a general character of polyps, disguised by their radiating form. Among the medussae something similar exists in the disposition of the marginal appendages and the ocelli. I attach the more importance to these observations, because they may lead to a clearer perception than we have yet reached