532 



A NATURALIST ON THE " CHALLENGER." 



is arrived at. These radiate cyclosystems in the Stylasteridce so 

 closely simulate in appearance the cups of ordinary Anthozoan 

 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 real significance. 



The two radiate calcareous structures are in reality widely 

 different in nature. In the Anthozoan coral, each radiate 

 system is the skeleton of one polyp animal like a single Sea 

 Anemone, and the radiating plates of calcareous matter in the 

 coral cup, are supports developed inside the body of this single 

 polyp. In the cylosystem of the Stylasterid, on the other hand, 

 a large number of polyps are lodged, namely a single gastro- 

 zooid and numerous dactozooids. 



The radiating plates of the cyclosystem, so like the septa of 

 Anthozoan corals, are formed of the walls of the mouths of the 



PORTION OF A SPECIMEN OF THE CORAL OF ASTYLUS SUBVIRIDIS. 



Showing the cyclosystems placed at intervals on the branches, each with a central gastropore and 



zone of slit-like dactylopores. 



dactylozooids pressed against one another as they are closely 

 packed together in a ring round the gastropore, and thus flattened 



