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



PLATE VIII. 



Fig. 1. Shows the structure of the soft parts of Astylus subviridis. A single cyclo- 

 system, divided in half, together with portions of the branch on which it 

 rests, is represented in the figure. At the lower part of the figure the large 

 ccenosarcal canals occupying the axis of the branch are seen passing right 

 and left. These place the cyclo-system in connection with the other 

 adjacent cyclo-systems on the branches of the coral. The gastrozooid, which 

 is devoid of tentacles, is seen resting retracted at the bottom of its sac (A). 



The base of the gastrozooid is rounded and basin-shaped. Large canals 

 spring from the margin of the basin to join the ccenosarcal meshwork, and 

 carry into the general circulation the products of digestion, but none such 

 arise from the direct under surface of the zooid. 



G Z. Cavity of the upper chamber of the sac of the gastrozooid. 



G Z. Cavity of the lower chamber of the sac of the gastrozooid. 



Z. The gastrozooid. 



0. The mouth appearing as a crucial slit with symmetrically arranged 

 elongate gastric cells. 



B. Tongue-like process of the wall of the gastropore which projects 



forwards horizontally over the summit of the retracted gastrozooid 

 at a point where there is a sudden constriction of the pore. The 

 projection of the tongue forms the opening of the constriction into 

 a horseshoe-shaped aperture. 

 D Z, D Z. Dactylozooids retracted into their pores, and doubled down 



into the mouth of the sac of the gastrozooid. 

 P, P. Mouths of the sacs of the dactylozooids, occupying in the recent 

 condition the dactylopores. These mouths are in this species 

 elongate in outline, and simulate the interseptal spaces of Anthozoan 

 corals. 

 G, G. Male gonophores in special sacs, and springing from branches of 

 the ccenosarcal network. 



C. Deep axial ccenosarcal canals of the branches of the coral on which 



the cyclo-systems rest. 

 S, S. Superficial networks of finer canals lying immediately beneath the 



superficial external layer of the ectoderm. 

 R, R. Radially disposed offsets of the ccenosarcal network springing from 



the sac of the gastrozooid. 

 X, X. Inter-radial spaces (cf. PI. VI. R R, X X). 



