PLATE XXVIII. 
Erylus formosus, 
Figure 1. Sponge; nat. size. 
„ 2. Vertical section passing through the middle of the cloaca; nat. size. (The section as repre- 
sented is turned sideways up.) 
J) 
3-13. Spicules — . 
Fig. 3. Oxea ; x 95. 
„ 4. Orthotrisene ; x 95. 
„ 5, 6. Sterraster ; x 95. 
„ 7. Soxnalcentrotylotemicrostrongyle; x 95. 
„ 8. Ohoanosomal oxyaster ; x 95. 
„ 9. Ohoanosomal oxyaster ; x 292. 
Fig. 10. Sterraster, x 292 ; 10a, transverse sec- 
tion of sterraster. 
„ 11. Sterraster, in the stage immediately 
preceding completion ; x 292. 
,, 12. A still younger form of sterraster; x 292. 
„ 13. Somal centrotylote microxea ; x 360. 
14. Tangential section through the cortex, showing transverse sections of the chones; x 14. 
15. Part of a vertical median section passing through the cloaca; x 14. 
1 6. Section at right angles to the surface of the sponge ; x 50. 
17. Part of the same, more highly magnified; x 125. 
18. Structure of the superficial part of the cloacal wall, just below the margin of the oscule; 
X 292. 
„ 19. Part of a section through the choanosome; x 225. 
„ 20. A pigment cell ; x 225. 
,, 21. Darkly staining cell, from which probably the pigment cell arises; x 292. 
„ 22. Pigment cell surrounded by sarcencytes; x 292. 
„ 23, 24. Problematical structures; x 292. 
„ 25. Epithelial cells seen in the walls of an excurrent canal; x 292. 
„ 26. Chiaster seen within its sclerohlast; x 292. 
„ 27, 28. Two forms of chiaster; x 292. 
„ 29. Chiaster situated beneath the epithelium of a canal, showing the tangential position of the 
actines; x 292. 
„ 30. The youngest form of sterraster observed ; x 292. 
,, 31. A young sterraster, showing the nucleus and immediately surrounding protoplasm of the 
sclerohlast; x 292. 
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