Miscellaneous. 73 



On the Development of the Spongillae. 

 By Dr. A. Gotte. 



The following statements relate to the Spongilla jluviatilis of the 

 harbour of Rostock, the developmental forms of which have been 

 investigated both intact and in sections. 



The segmentation leads to the formation of a sterroblastula, the 

 cells of which are not placed radially around a central point, but 

 irregularly in several layers, and at first present no regular distinc- 

 tion of sizes. The latter makes its appearance comparatively late, 

 when the peripheral cells in one hemisphere diminish rapidly and 

 close up into the form of a membrane. Gradually a thin cylinder- 

 epithelium is developed from this, and it completely surrounds the 

 remaining coarsely cellular mass. Thus is produced a completely 

 closed sterrogastrtda, with an epithelial ectoderm and a moderate 

 endoderm. 



The cells of the former gradually become smaller, and it is at last 

 ciliated. In the middle of the endoderm a cavity is produced by the 

 separation and not by the fusion of the cells, and this is enlarged 

 towards the broader end of the oval gastrula, and finally passes into 

 it altogether. By this means the endoderm in this anterior or 

 superior hemisphere (according to the subsequent position of the 

 larva) becomes a thin loose layer applied to the ectoderm, archin°- 

 over the cavity and attached by its margin to the posterior thick 

 mass of endoderm. 



In this state the larva escapes, and after a time attaches itself by 

 the anterior end. In this process the ectoderm is ruptured, and the 

 amoeboid endorlermal cells, reticulately united, attach themselves to 

 the supporting body. By a simple continuation of this process the 

 whole endoderm spreads into a flat cake, upon which the torn and 

 already partially detached ectoderm rests loosely like a mantle ; or 

 the larva, after the first attachment, lies down upou the whole of 

 its side-length, so that a part of the ectoderm comes to lie under 

 the cake of endoderm. The whole organism then usually slips away 

 from this basal disk of endoderm, leaving it to dissolve ; in other 

 cases it disappears by atrophy of the endodermal mass. The super- 

 ficial ectodermal mantle, below the margin of which, all round, the 

 attachment by means of the amoeboid endodermal cells takes place, 

 usually breaks up into larger and smaller pieces which are ex- 

 foliated ; or it disappears by atrophy, the cells and nuclei becoming 

 indistinct and finally disappeai-ing, so that the underlying endoderm 

 is freely exposed. 



About the time of the escape of the larva (but the sequence of 

 all the developmental phenomena of the Spongillce is remarkably 

 variable), the transformation of the endoderm with the excentnc 

 cavity commences. By the flattening and extension of the cells of its 



Ann. & Mag. N, Hist. Ser. 5. Vol xv. 6 



