Postlarval Development of Leucosolenia variabilis, H. sp. 47 



of the larva, and its nucleus is usually, but not always, elongated in 

 the same direction, so as to have a rod-like form. The whole struc- 

 ture, with pigment, lens-like body, and central granular cells, gives 

 strongly the impression of a primitive, light-perceiving organ. The 

 pigment itself is lodged in the inner ends of the ciliated and inter- 

 mediate cells, and is, no doubt, the same pigment as that observed by 

 Metschnikoff* and Schulzet in the inner ends of the ciliated cells in 

 the larva of Sycandra raphanus. As the intermediate cells pass into 

 the condition of granular cells, they leave the pigment behind, so 

 that the pigment is thickest in the region of the intermediate cells, 

 at the sides of the lens-like body. 



The larva is thus composed of four kinds of cells, which may be 

 termed the ciliated, intermediate, granular, and central cells. Since 

 the intermediate cells are merely a transitional form between the 

 ciliated cells proper and the granular cells, we have to reckon with 

 three classes of cells only in the fully developed larva. 



The fixation takes place by the anterior pole of the larva, and the 

 granular cells grow round the ciliated cells. The metamorphosis is 

 complete in a few hours. Sections of fixed stages of the first day of 

 fixation (fig. 4) show them to be composed of two very distinct cell 



Fia. 4. Section of larva shortly after fixation, the metamorphosis not quite 



complete. 



layers : (1) a compact central mass of cells, easily recognisable, by 

 their opaque, irregularly shaped nuclei and vacuolated cell protoplasm, 

 as the former ciliated cells, surrounded by (2) a single layer of 

 flattened epithelial cells, the former granular cells of the larva. . No 

 trace is to be found of the central cells, which appear to be thrown 

 out together with the pigment, at the metamorphosis. The inner 

 mass is" the future gastral layer of the sponge, the outer epithelium 

 the future dermal layer. 



* Zur Entwicklungsgeschichte der Kalkschwamme," ' Zeitschr. f . Wiss. Zool,' 



V f " Ueber den Bau u'nd Entwicklung von Sycandra raphanus," ib., vol. 25, suppl., 

 pp. 247-280, Taf. XVIII-XXI. 



