510 MB. H. M. BEENAED ON ALTEOPORA. 



Fig. 2-2 a. Views from the side, and from above of a later stage in which the 

 colony consists of three or four polyps contained within the same 

 epitheca. 



3. View from above of a still later stage. 



4. Transverse section of a specimen of the TBlseozolo Famsifes gothlajidica, 



showing the black median line in the walls, which can here and there 

 be seen to run into the septal spines and at the angles to form stars. 



5. Transverse section of a recent Alveopora, showing the same black line 



in the walls and running into the septal spines. 



6. Diagram of an early evolutionary stage in the Madreporarian skeleton 



{cf. figs. 1-1 d), an epithecal cup with septal spines ; the bud appears 

 over the rim of the epitheca. The thickness of the epitheca in this and 

 the following diagrams is purposely exaggerated. 



7. The septa are laminate. 



8-9. The laminate septa have risen above the rim of the epithecal cup and 

 have fused by means of local thickeniugs (shaded areas). The epitheca 

 becomes vestigial, the new internal wall formed by the fused local 

 thickenings of the septa, called the theca, divides the primitive se]:)ta 

 into septa and cost^e. The portion of the body of the polyp which 

 covers the costse is called the " edge-zone " or " Eandplatte," and the 

 buds develop from it. 



10. Diagram of the parent polyp of an Astrseid colony (as here limited) ; 



the new internal wall or theca, which supports the septa, is here 

 formed of dissepiments. 



11. Sketch (X 7) of the skeleton of a polyp showing overflowing of the 



epithecal wall by the septal portion of the skeleton {cf. text, p. 513). 



