On the Development of the Galcispongise. 41 II. — On the Development of the, Calcispongige. By Elias Metschnikoff*. [Plate II.] During my residence at Messina in the spring of 1868 I made some observations on the development of Sycon ciliatum {Sycandra raphanus. Hack.), which I have not hitherto pub-lished, because I did not consider them sufficiently completef. But now, since the appearance of Hiickel's ' Monograph of the Calcispongia? 'J, I feel compelled to publish my investiga-tions. The reasons which have moved me to hesitate no longer in doing this will be clear enough from what follows. I hope that my memoir, small as it is, will not be passed unnoticed by the readers of Hackel's three-volume monograph, inasmuch as it is devoted exclusively to developmental history, i. e. to that department of zoology the great importance of which in morphological questions seems to be now generally recognized. With regard to the special case before us, that of the Calcispongia?, the important part of developmental history is strongly insisted upon by Hackel ; but unfortunately the investigations of that naturalist relating to this subject are so defective that a fresh treatment of the matter has become a pressing necessity. I pass now to the description of my investigations. When we examine transverse sections of sexually mature Syca, we observe beneath the entodermal lining a great number of ova and embryos in very different stages of development. The total and regular segmentation takes place in the same way as is described by Hackel in Sycyssa Huxleyi and Leucul-mis echinus. We have only to remark that a small so-called segmentation-cavity (PI. II. fig. 2, c) is formed, which, how-ever, soon disappears (fig. 3). As the result of the process of segmentation a roundish embryo (fig. 4) is produced, on which a great number of small cells are to be detected. I could not succeed in discovering any process of differentiation in the embryo, for which reason the question of the origin of the germ-lamella? must remain undecided. Evidently the stages are too quickly passed through for them to be accurately observed. I must therefore pass on at once to the description * Translated by W. S. Dallas, F.L.S., from the ' Zeitschrift fur wissen-schaftliche Zoologie,' Baud xxiv. (1874), pp. 1-14, pi. i. t I have already given a short account of them iu my annual report upon the progress of developmental history, printed in Russian. \ f Die Kalkschwamme : eine Monographic.' 3 vols. Berlin, 1872. In this paper I shall only quote the lirst volume of this work
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