CALCAEEOUS SKELblTON OF THE ANTHOZOA. 



523 



described by Mrs. Gordon. But centres of calcification are 

 clearly present, though not represented by dark spots. The 

 section clearly shows radiating systems of crystals diverging 

 from centres a, a, the latter appearing white and translucent 

 when viewed by transmitted light. From these centres crys- 

 talline fibres diverge upwards and outwards, spreading out to 

 greater distances from the centre in three positions, which are 

 approximately at 120° to one another. These extensions meet 

 and dovetail with similar extensions from adjoining centres, 

 and thus produce the characteristic skeleton of the coenen- 

 chymal tubes. The section figured is not from the extreme 

 growing point, but rather below it. At the extreme growing 

 point it would be seen that each centre is really trifid, pro- 

 ducing the arrangement which 1 have described before, and 

 which I need not further particularise. A little below the 

 extreme growing edge the separate centres unite in the angle 

 formed between three adjacent coenenchyraal tubes, and there 

 form a more or less Y-shaped centre of calcification, from 

 which the crystalline fibres diverge in three directions, meeting 

 in sutural junctions with similar diverging systems with the 

 diverging fibres from adjacent systems. The whole structure 

 is displayed in the annexed diagram. From this it is seen 



Diagram illustrating the arrangement of the crystalline fibres forming the 

 corallum in Heliopora coerulea. ct. Coenenchymal tubes, tr. Tra- 

 beculae. s. Sutures. 



VOL. 41, PART 4. NEW SKBIES, O O 



