212 THE VOYAGE OF H.M.S. CHALLENGER. 



the border behind this wall all round a narrowed prolongation of the 

 lower chamber of the gastropore passes up, and leads above by a series 

 of offsets to the lower terminations of the tubular portions of the dactylo- 

 pores, conveying, in the recent condition of the coral, the main canals 

 springing from the gastropore. The support of the lid of the pore system 

 sends a stout prolongation downwards to fuse with the wall of the upper 

 chamber of the gastropore. 



G P. Upper chamber of the gastropore. 



G P\ Lower chamber of the gastropore. 



D P, D P. Dactylopores. 



C. Space behind the wall of the upper gastropore chamber leading to the 



dactylopore tubules. 

 L. Lid covering the cyclo-system. 

 Fig. 8. Pore system of Astylus subviriclis laid open by a vertical incision through the 

 axis and in the direction of the length of the supporting branch. 

 G P. Upper chamber of the gastropore. 

 G P'. Lower chamber of the gastropore. 



B. Tongue-like process of the lower border of the wall of the upper 

 chamber of the gastropore, which projecting horizontally in the 

 direction, in each system, of the tips of the branches, converts the 

 aperture leading between the two chambers into the form of a 

 horseshoe. 

 A. Base of the tongue-like process and part of the wall of the upper 

 chamber cut through. 



O 



C C. Space behind the wall of the upper gastropore chamber, leading, as 



in the last figure, to the dactylopores. 

 G, G. Ampullar 

 Figs. 9-16. Diagrammatic representations of the arrangements of the gastropores and 

 dactylopores in the several genera of Stylasteridre, to show the manner 

 in which cyclo -systems and their r seudosepta have become developed in this 

 family. 

 The following letters apply similarly throughout the series : — 

 G Z. Gastropore. 

 S. Its style. 

 D Z. Dactylopore. 

 Fig. 9. Sporadopora dichotoma. The pores of both kinds are irregularly scattered over 



the surfaces of the ccenosteum. 

 Fig. 10. Allopora nobilis. A number of dactylopores are grouped in a circle around a 

 single centrally placed gastropore. 



