O PHYSIOLOGICAL SERIES. 



Structure and Mode of Formation, 

 Continuous, non-spicular. 



A. 20. Caryophyllta prqfunda, one in section and the other entire, 

 as an example of a simple aporous Coral, with diagram. 

 The sea-anenome-like polyp first secretes upon the rock to 

 which it is attached a disc-like basal plate ; radiating ridges 

 on the upper surface of this enlarge to constitute the septa, an 

 extension of the outer ends of these grow together to form 

 the theca, and an elevation in the centre is known as the 

 columella. The corallum, although external to the polyp, 

 functions as a deep-seated support. PI. I. fig. 2. 



G. v. Koch, Mitth. Zool. Sttit. Naples, Bd. xii. 1897, 

 p. 767. 



A. 21. A simple, free, aporous Coral (Fungia actiniformu), with 

 diagram. It results from the detachment of the enlarged 

 free end of a fixed coral resembling the preceding specimen. 

 The septa are united by calcareous bars (synapticulffi), which 

 contribute to the strength of the coral. PI. II. fig. 1. 

 Bourne, Q. J. Micr. Sci., vol. xxvii. 1887, p. 293. 



A. 22. A compound aporous Coral (Podllopora cespitosa), with 

 diagram. The corallum is composed of tubes whose sides 

 are in contact. The cup-like end of each tube lodges a 

 polyp, the bottom of the cup is formed by a plate (tabula). 

 The tabulse are formed whenever the cup becomes too deep 

 from additions to its lip. The digestive cavities (coelentera) 

 of the polyps communicate with one another by canals 

 (ccelenteric canals). PI. II. fig. 2. 



A. 23. A fossil Coral (Favosites gothlandica). The tabulae are 

 very distinct. Brit. Mus. 



A. 24. Blue Coral (Heliopora ccerulea, Order Alcyonaria), and 

 diagram illustrating its structure. The corallum consists of 

 tubules of two sizes. In the larger are lodged the polyps, 

 each having eight pinnate tentacles ; the smaller lodge 

 tubular extensions of the digestive cavity of the polyp 



