PLATE XVII. 
Tribracliium sehmidtii. 
Figure 1. Several examples of the sponge; nat. size. 
„ 2-8. Spicules — 
Fig. 2. Oxea ; x 32. 
„ 3. Somal ortliotrisene ; x 32. 
,, 4. Anatrisene ; x 32. 
,, 5. Cladal end of an anatrisene ; x 292. 
Fig. 6. Cladal end of an anatrisene, reduced 
to an anamonsene ; x 292. 
,, 7. Cloacal ortFodisene ; x 32. 
,, 8. a-d, various forms of sanidaster; c, 
closely approaches a chiaster ; x 576. 
9. Vertical median section through the body of the sponge, including the hasal portion of the 
cloacal tube ; x 7, 
10. A part of the preceding, more highly magnified to show the passage of the cloacal tube into 
the body; x 15. 
11. The skeleton of the basal part of the cloacal tube seen en face ; x 49. 
12. Longitudinal transverse section through the base of the cloacal tube, showing the develop- 
ment of the orthodisenes ; x 300. 
13. Part of a transverse section through the base of the cloacal tube and surrounding choanosome 
of the sponge body. The part of the figure below “13 ” represents the tissue of the cloacal 
tube ; X 15. 
14. Part of the preceding, showing the arrangement of the spicules of the cloacal tube in radial 
series, the youngest spicules being situated nearest the exterior (lower part of the figure) ; 
X 180. 
15. Longitudinal section through the cloacal tube, showing the general disposition of the soft 
parts; x 15. 
16. Longitudinal hut not median section through the cloacal tube, cutting the inner wall 
tangentially; x 15. . 
17. Transverse section through the base of the cloacal tube and surrounding sponge; dicho- 
trisenes occur in this region, but nowhere else; x 15. 
18. Transverse section through the cloacal tube ; x 15. 
19. A single example of an oxyaster observed within its scleroblast ; x 430. 
20. The youngest example of orthodisene observed, seen within its scleroblast ; x 300. 
21. One of the granule cells which occur somewhat abundantly scattered through the choano- 
some ; X 292. 
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