PLATE VI. 
Figs. 1-9. Thenea wyvillii , ... 
Figure 1. Sponge ; nat. size. 
„ 2. The “ pileus,” seen from above, showing the characters of the oscule ; 
nat. size. 
,, 3-8. Spicules — 
Fig. 3. Promonasne, or plagiomonsene ; 
X 22. 
4. Dichotriaene ; x 22. 
6. Somal anatrisene ; x 180, 
Fig. 6. Cladal end of radical anatriaene ; 
X 180. 
„ 7. Metaster x 360. 
„ 8. Plesiaster; x 49. 
9. Transverse section through a part of the sponge, showing the ectosome 
and characters of the choanosome ; x 49. 
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74 
Figs*. 10-20. Thenea delicata, 
„ 10. Sponge; nat. size. 
„ 11, 12. Spicules. 
Fig. 11. Eadical oxytylote j x 32. 
Fig. 12. Tylote end of the preceding; 
X 180. 
,, 13. Median vertical section through the sponge ; nat. size. 
,, 14-16. Vertical sections taken successively nearer the edge; nat. size. 
„ 17. Section through the choanosome, showing the flagellated chambers; 
X 180. 
60 
1 8. Section through the wall of the cloaca near the margin of the oscule, 
to indicate the position of the tissue which is shown on a larger 
scale in the succeeding flgure. 
19. Section of a part of the wall of the cloaca, containing reserve cells 
(thesocytes) ; x 360. 
20. Section through two flagellated chambers, one of them in a state of 
contraction, showing flne fllaments proceeding from the choano- 
cytes into, the surrounding tissue ; x 360. 
Figs. 21, 22. Thenea grayi, . . .65 
21. Vertical median section through the sponge ; x 2. 
22. Sponge ; nat. size. 
