No. 3-] DEVELOPMENT OF MAREXE SPONGES. 293 



20". The egg-cell has always a large nucleus with a very large 

 nucleolus. In the cytoplasm there are usually several deeply 

 staining bodies, each surrounded by a clear space. One of 

 these bodies in Fig. 20" is quite large. The bodies stain as 

 deeply as chromatin, and I suspect them to be the remnants 

 of engulfed cells. The occurrence of such bodies in the 

 cytoplasm coupled with the fact that the outlines of the egg- 

 cell are often indistinct in spots, suggests that the ovum is 

 feeding on the surrounding mesoderm cells. In a very few 

 cases I have met an egg-cell in the peculiar situation illustrated 

 by PI. XV, Fig. 20'". A gemmule, g, of about full size, is only 

 partially surrounded by its follicle. The bare portion is con- 

 tinuous with a thickly packed mass of mesoderm cells, in which 

 lies the egg-cell, o. ov. PI. XVI, Fig. 20", is a more highly 

 magnified view of the bare end of the gemmule, The gem- 

 mule cells, g, fade away into the less densely packed mesoderm 

 cells, in the midst of which is the ovum, o. ov., surrounded by 

 a follicle, ov. f., which was not present in the egg shown in 

 Fig. 20". It seems pretty clear that the gemmule, g, after 

 reaching its full size, burst or absorbed its follicle and became 

 continuous with the surrounding mesoderm. Only these very 

 small egg-cells are met with, but they serve to indicate that a 

 se.xual breeding season follows the gemmular season. 



In this connection I may speak of certain gemmule-like 

 bodies, which I am unable to explain, but which resemble a 

 stage in spermatogenesis more than anything I know of. (See 

 Fiedler's figures for Spongilla, 5, and those of Vosmaer for 

 Leucosolenia, 33, Taf. x.xix.) Two of these problematical bodies 

 are shown in PI. XV, Fig. \'j,pr. g., and another in PI. XV, 

 Fig. 14. They are comparatively common. They consist of a 

 follicle inside which are small spherical cells entirely free from 

 one another. The substance of these cells, if cells they are, 

 stains feebly and appears homogeneous, and to the outer sur- 

 face of each clings a crescentic band of chromatin. These 

 bodies are always of small size, like those shown in Figs. 14 

 and 17. Their size and follicle suggest that they are derived 

 from gemmules. At first I thought they were degenerating 

 gemmules, but their uniform appearance scarcely admits of this 



