PLATE XXX. 
Theonella swinhoei, ..... 
Figure 1. Part of a vertical median section through a small example of the sponge; on the right the 
collenchymatous wall of the cloaca, on the left the ectosome, between them the choano- 
some; x 10. 
„ 2. Tangential hut slightly oblique section through the ectosome, showing on the lower margin 
the pore areas, and above them the ramifying suhdermal cavities ; x 10. 
,, 3. Tangential superficial slice, showing two groups of pores ; x 95. 
„ 4. A single pore : the surrounding epithelium appears as a nucleated membrane, below it are 
scattered microstrongyles ; x 360. ' 
„ 5. Section at right angles to the surface ; the darker portion represents the ectosome, the lighter 
the choanosome ; x 20. 
„ 6. Section at right angles to the surface through the roof of a chone ; x 430. 
„ 7. Section through the choanosome, showing the characters of the chamber system, on the right 
a strand of fusiform cells ; the linear series of dots in the choanosome indicate Oscdlaria ; 
X 180. 
„ 8. Part of the preceding more highly magnified ; x 700. 
„ 9. A nearly longitudinal section through a canal, showing the collenchymatous walls ; x 49. 
„ 10. A similar hut transverse section ; x 49. 
„ 11. Part of the preceding section, more highly magnified ; x 300. 
„ 12. Part of the choanosome, containing parasitic cells ; x 430. 
„ 13. Longitudinal section through a fibrous strand; on the left epithelial cells, on the right 
associated Oscillaria are seen ; x 360. 
,, 14. Similar to fig. 12 ; x 430. 
„ 15. Epithelium, showing cellular outlines, from the walls of a canal; x 540. 
„ 16. Similar, but with the cells isolated ; x 540. 
„ 17. A section through the choanosome, showing strongyles' in situ, with associated spongin, 
indicated by the darker tint ; x 95. 
„ 18. A cell occupying the interspace between the syzygial tubercles of two desmas ; x 360. 
„ 19. A desma, indicated by the untinted part with a blue outline, showing the sclerohlast in situ 
over the centre ; x 430. 
„ 20. The young crepis of a desma seen embedded in its sclerohlast ; x 292. 
„ 21. Similar, but the crepis still smaller, and presumably younger ; x 292. 
„ 22. Tissue replacing the collenchyma in some parts of the sponge ; x 540. 
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