34^ ir/LSOx. [\-0L. IX. 



of quite small spheres, but scattered about in the fine yolk are 

 certain large rounded bodies which I take to be the first large 

 spheres formed. 



While the egg is still small, long before it reaches the full 

 size, the single nucleolus gives place to two nucleoli periphe- 

 rally placed, as in PI. XXIII, Figs. 115 and 115'. The e.gg of 

 PL XXIV, Fig. 116, has likewise two nucleoli, situated in the 

 same way, but the section passed through only one of them. 

 Between the two nucleoli there is a sphere of granular mate- 

 rial, which stains much less deeply than the nucleoli them- 

 selves, and which is separated from the nuclear membrane by 

 a clear space. When the egg attains its full size, one of the 

 nucleoli is lost, leaving no perceptible trace behind. In the 

 nucleus thus left with a single nucleolus. Fig. 117, the nuclear 

 membrane could not be made out in my preparations, though 

 the sphere of faintly staining granular material was obvious. 

 Fig. 118 (portion of the periphery of such an egg as that of 

 Fig. 117). The second nucleolus is then extruded, and may 

 be seen lying in the yolk in the immediate neighborhood of 

 the nucleus, which now consists exclusively of the sphere of 

 granular material, separated from the yolk by a narrow clear 

 space. Fig. i iS. 



Segmentation results in the formation of a solid morula. 

 An early stage in the segmentation is shown in the section, 

 Fig. 120, and two morulas are shown in Figs. 121, 122. In the 

 latter morula one of the segmentation spheres has been retarded 

 in its division, and is consequently of a much larger size than 

 the rest. Scattered between the segmentation spheres and 

 forming a layer round them, there will be noticed a peculiar 

 granular stuff which stains feebly but which is very conspicuous 

 in the sections. It is probably a precipitate from the fluid bathing 

 the segmentation spheres, caused by the fixing fluid (Perenyi). 



V. Remarks on the Morphology of Sponges.^ 



I have shown that in Esperella and Tedania the subdermal 

 cavities, canals, and chambers develop as separate lacunae in 



1 The figures which illustrate this article, excepting Fig. 5, are borrowed. For 

 their sources see description of the plates. 



