462 



TAHITI. 



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 cyclosystem of the Sty/asferid, on the other 

 hand, a large number of polyps are lodged, namely a single 

 gastrozooid and numerous dactylozooids. 



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

 Anthozoan corals, are formed of the 

 walls of the mouths of the dactylo- 

 zooids pressed against one another 

 as they are closely packed together in 

 a ring round the gastropore, and thus 

 flattened out by mutual appressure. 

 The elongate or groove-like form of 

 the mouths of the pores is also to a 

 large extent brought about by the 

 manner in which the dactylozooids 

 are doubled up within them when in 

 the retracted condition. 



The accompanying figure repre- 

 sents a small part of the skeleton or 

 coral of a stock of Astylus subviridis, 

 enlarged to twice the natural size. 

 The cyclosystems, one of which is 

 shown as a diagram in Fig. 6 of the 

 preceding woodcut, are here seen 

 placed at intervals along the branches 

 of the coral. 



Still further complexity, however, 

 in the cyclosystems of the genus 

 Astylus remains to be described. The 

 figure on the opposite page shows one 

 of the systems cut through vertically to 

 display the arrangements within, i'he 

 gastropore has two chambers, an upper 

 and lower. The lower, in which the 

 gastrozooid, which in this genus is a mere flask-shaped stomach 

 sac devoid of tentacles, is lodged, communicates with the upper 

 by a narrowed horseshoe-shaped opening, which is more plainly 

 seen from above in the diagram. Fig. 6, already referred to. The 

 opening is rendered horseshoe-shaped by the projection from 

 one side of it across the aperture of a small tongue-shaped 

 excrescence of hard coral. This projection no doubt serves 

 to protect the polyp from injury. 



PORTION OF A SPECIMEN OF 

 THE CORAL OF ASTYLUS 

 SUBVIUIDIS. 



Showing the cyclosystems 

 placed at intervals on the 

 branches, each with a central 

 {rastropoie and zone of slit- 

 like dactylopores. 



