Chap. XX.] 



STRUCTURE OF ALLOPORA 



461 



tentacular zooids to feed the mouth-bearing zooid in the 

 gastropore. 



A more complete development of radiate systems occurs in 

 another species of Allopora (A. profunda), as shown in Fig. 4. 

 Here 12 dactylopores surround each gastropore, and the 

 grooves are much deepened. The dactylopores in this case 

 have small rudimentary styles, which structures are usually 

 confined to the gastropores. In Allopora miniacea (Fig. 5), 

 the styles in the dactylopores are large, and have brush-like 

 tips like the styles of the gastropores. 



DIAGRAMS ILLUSTRATING THE SUCCESSIVE STAGES IN THE DEVELOPMENT OF 

 THE CYCLOSYSTEMS OF THE STYLASTERID^. 



I In Spoi-adopora dichtoma. 2, 3 Allopora nobilis. 4 Allopora profunda. 

 5 Allopora miniacea. 6 Astylus subviridis. 7 Distichopora coccinea. 

 i- Style; dp dactylopore ; V> gastropore; d in fig. 6, inner horseshoe- 

 shaped mouth of gastropore. 



In the genus Astylus, neither kind of pore has a style, the 

 radiate arrangement is most complete, and the highest condi- 

 tion of development of the circular systems of zooids (cyclo- 

 systems) is arrived at. These radiate cyclosystems in the 

 Sfvlasterida' so closely simulate in appearance the cups of 

 ordinary Anlhozoan corals with their radiate septa, that they 

 were always supposed to be of the same essential nature as 

 these'latter, until dissection of the soft structures of the animals 

 of which they are the skeleton, revealed their rcnl significance. 



