176 E. JR. Cuming s — Development of Fenestella. 



Plate V. 



Figures 1-16. — Transverse serial sections of a Fenestella base. These six- 

 teen sections represent l mm thickness of rock. 



Figures 1, 2.— Protceciuin (cf. figs. 40, 41, 31-35). 



Figure 3. — Section in the plane of a-a, figure 47, cutting the proximal ends 

 of the primary buds and the buds of the second generation (secondary 

 buds) (cf. fig. 42). 



Figures 4, 5.— Successively higher sections. 



Figure 6. — Section in plane of a'-a' , figure 47, cutting the proximal end of 

 the tertiary bud (cf. fig. 43). 



Figures 7-12. — Successively higher sections between the planes of a'-a' and 

 c-c, figure 47, showing the development of the initial buds. Figures 

 10-12 cut the aperture of the ancestrula (cf. fig. 24. with fig. 12). 



Figure 13. — Section cutting the proximal ends of buds of the second tier 

 (IZii., IIsi, Illb, and IIIc) (cf. fig. 26). 



Figure 14. — Section just cutting the distal end of the aperture of the 

 ancestrula. 



Figures 15, 16. — Assumption of the star-shaped arrangement of zocecia, 

 characteristic of the paranepiastic stage of Fenestella. 



Plate VI. 



Figure 17. — Longitudinal section of a Fenestella base cutting in the plane 

 of e-e, figure 47, and a-a, figure 48. This section passes through the 

 edge of the protoecium and misses the ancestrula entirely, 6, b', buds 

 of the second tier. At z and z' the zocecia are vertically above each 

 other; at z", z'" they alternate, and at the top of the figure they lie side 

 by side, x 17. 



Figure 18. — Longitudinal section cutting still more excentrically than that 

 shown in figure 17, probably in the plane of 6-6, figure 48. This misses 

 the protcecium and ancestrula entirely, but their relative- position is 

 shown at o and A. The vertical alignment of zocecia is shown at z-z / 

 and the ordinary arrangement, on either side of the carina, at z". The 

 bifurcation of a primary branch is shown at g-h (between z" and g, h). 

 In each new branch, the zocecia first alternate and later lie side by side. 

 Normal arrangement shown at k' k". x 17. 



Figure 19. — Longitudinal section cutting in the plane of c-c, figure 48. The 

 section cuts a row of zocecia {z'-z") nearly longitudinally. x 17. 



Figure 20. — Section in nearly the same plane as in figure 19 (d-d. figure 48). 

 This section was orientated by polishing and etching the basal surface of 

 the colony and marking the position of the protcecium and primary 

 buds. The section was then ground as nearly as possible in the marked 

 direction. A primary bud is very clearly shown (/). x 17. 



Figure 21. — Transverse section in the plane of a-a, figure 47. The primary 

 buds are very distinct, x 17. 



Figure 22. — Similar section of another specimen, cutting the proximal end 

 of the ancestrula. x 17. 



Figure 23. — Transverse section of a very slender base. Section in about 

 the same plane as 22. x 17. 



Figure 24. — Section in the plane of 6-6, figure 47. Ancestrula very dis- 

 tinct, x 17. 



Figure 25. — Longitudinal section of a base from which the substratum was 

 absent, x 17. 



Figure 26. — Transverse section in the plane of d-d, figure 47, showing the 

 proximal ends of two buds of the second tier (z, z') (cf. fig. 13). x 17. 



Figure 27. — Protcecium and ancestrula of Retepora phoenicea from St. 

 Vincent's Gulf, Australia, x 27. 



Figure 28. —Ancestrula and three primary buds (1, 2, 3) of Retepora phce- 

 nicea. x 29. 



Figure 29. — Profile view of protcecium and ancestrula of another specimen 

 of Retepora phoenicea. x 27. 



