Amongst other calcareous sponges the larva of _Ascandra contorta_ (Haeckel No. 126, Barrois No. 122) presents the typical amphiblastula stage, and so probably does that of _Ascandra Lieberkühnii_ (Keller No. 128). In _Leucandra aspera_ (Keller No. 128, Metschnikoff No. 134) the larva passes through an amphiblastula stage, but the characters of the cells of the two halves of the larva do not differ to nearly the same extent as in Sycandra. Although the majority of calcareous sponges appear to agree in their mode of development with Sycandra, nevertheless the concordant researches of O. Schmidt (No. 138) and Metschnikoff (No. 134) have shewn that this is not true for the genus Ascetta (_As. primordialis_, _clathrus_ and _blanca_). The larvæ of these forms are very differently constituted to those of Sycandra. They have an oval form and are composed of a single row of ciliated columnar cells: their two extremities only differ in the cells at one extremity being longer than those at the other. Especially at the pole where the shorter cells are situated (Schmidt) a metamorphosis of the cells takes place. One after the other they lose their cilia, become granular, and pass into the interior of the vesicle. Here they become differentiated into two classes (Metschnikoff); one of larger and more granular cells, and the other of smaller cells with clearer protoplasm. Cells of the former class are mainly found at one of the poles. When the larva becomes free the cells in the interior of the vesicle increase in number and nearly fill up its central cavity. After a short free existence the larva becomes fixed, and the epiblast cells lose their cilia and become flattened. At a later period the large granular cells assume a radiate arrangement round a central cavity and become clearly marked out as the hypoblast cells. The smaller cells become placed between the epiblast and hypoblast and constitute the mesoblast. Myxospongiæ. In this group Halisarca has been investigated by Carter (No. 123), Barrois (No. 122), Schulze (No. 141) and Metschnikoff (No. 134). The ova develop in the mesoblast, and when ripe occupy special chambers lined by a layer of epithelial cells. Schulze has found the spermatozoa of this genus of sponge and has been able to shew that the sexes may be distinct, though many species of Halisarca are hermaphrodite. The segmentation is, roughly speaking, regular, and a segmentation cavity is early formed, which is never, as in Calcispongiæ, open at the poles. When the larva leaves the parent it is an oval vesicle formed of a single layer of columnar ciliated cells. Slight differences may be observed between the two extremities of the larvæ of most species. One of these--the hinder extremity--is directed backwards in swimming.