A. General, 3. Embryology. 7 



strings of cells. - - The canals are lined by flat Bildungszellen, the subdermal 

 space is formed by the epidermis detaching itself from the internal mass, carried 

 on spicules. No cuticle was observed. - - The author has read Maas's paper [see 

 Bericht f. 1893 Porif. p 5], but cannot yield on the points of difference. 



Wilson considers it likely that the Espcrella larvae observed by Maas were the 

 product of gemmules, and this doubt must attach also to larvae described by 

 Schmidt and Vosmaer. Such larvae were observed for Esperella Jibrexilis n. and 

 Tedania Brucei n. E. in the summer shows many gemmules, the youngest 

 stages consisting of a small number of polygonal cells surrounded by a follicle of 

 flattened cells. A few small egg-cells were observed, they serve to indicate that 

 a sexual breeding season follows the gemmular season". There are many groups 

 of pareuchym cells closely similar to those composing the gemmules ; rarely such a 

 group may arise from division of a single cell : their cells appear to multiply by 

 division, the gemmules also increase in size by fusion with each other: degenera- 

 tion of the normal tissue accompanies their formation. The ripe gemmule is a 

 large cell aggregate; analogously to segmentation in an ovum this breaks into 

 smaller cell aggregates, which divide further and further until there results a 

 mass of single cells separated by interstitial jelly. The superficial cells are 

 differentiated into a coherent layer which becomes the ectoderm of the free 

 larva, columnar and flagellate except over the posterior pole; the interior cells 

 form the parenchyma, or mesentoderm: the latter consists mainly of fusiform 

 cells anteriorly; plump, finely granular, well-stained formative cells united by 

 processes in the middle; weakly-stained polygonal cells posteriorly, with oxytylote 

 and bow-shaped spicules and rosettes of shovels. Besides the larva-producing 

 gemmules there are gemmule-like bodies consisting of a follicle containing small 

 separate spherical cells, resembling a stage in spermatogenesis. The gemmule of 

 T. never showed either cell-outlines or nuclei, it is densely and uniformly 

 granular, the granules being fine yolk granules staining strongly witli all stains 

 used : the formation of an embryo proceeds as in E. ; the larva is at first com- 

 pletely covered with columnar flagellate cells, the characteristic bare posterior 

 area of low epithelium appearing later; the larval spicules are tylotes with nicked 

 heads. - Metamorphosis. The larva of E. is stated to fix by a point 

 near its posterior pole (no section showing this is given, larvae are described as 

 fixing on the water-surface by the anterior pole, and T. is said to fix near its 

 anterior pole) . The flat ectoderm of this region encroaches on the columnar 

 ectoderm, which partly migrates into the interior: the ectoderm subsequently 

 forms the transparent edge round the larva. Delage's epidermic cells were never 

 seen ; nor were the canals lined by cells which could be immigrated flagellate 

 cells. The formative cells of the mesentoderm arrange themselves round lacunae 

 which become subdermal cavities and canals. Many formative cells are multinu- 

 cleate, possessing a central larger nucleus with membrane and chromatin mass, 

 and one or more peripheral nuclei, each with its chromatin mass, nucleoplasm, 

 and surrounding membrane ; the author considers the central nucleus to have 

 given rise to the peripheral nuclei; the cell also contains bodies probably yolk- 

 granulestr, staining like chromatiu balls. Flagellate chambers arise by 

 formative cells grouping themselves into a hollow sphere, and multiplying by 

 division; also from cavities appearing in solid masses of small cells derived by 

 division from formative cells; the chambers sometimes occur in larvae before 

 metamorphosis. The dermal membrane is composed of ectoderm, mesoderm, 

 and the epithelial roof of the subdermal cavity ; oscula and pores arise as per- 

 forations in it. - The development of Tedanione n. foetida n. is similar; on two 

 occasions a larva was observed to divide and form two sponges. The only 



