in] SCYPHOZOA 75 



The so-called organ-pipe coral is, as has been already explained, 

 an Alcyonarian in which the spicules cohere. Various fossil so- 

 called corals, e.g., Syringopora, belong to the same category. The 

 red Neapolitan coral of which ornaments are made is also an 

 Alcyonarian, the spicules of which are of a bright pink or red 

 colour and cohere to form a rod in the axis of the colony. In some 

 spots off the coast of Australia the Alcyonaria with coherent spicules 

 are so numerous that they form reefs. 



Coral-forming anemones are found all over the world one 

 genus, Caryophyllia, being actually found at low spring tides on 

 the south-west coasts of England : but it is only in the tropics that 

 those species are found which keep on budding and growing with 

 sufficient persistence to build up the great reefs which form the 

 famous coral islands of warmer seas. Of course as soon as the 

 reef is built up to the surface the polyps cease to grow, and then 

 the breakers soon pile up broken off pieces in sufficient quantity to 

 raise the reef above the tide-marks. 



A third group of the Coelenterata is constituted by the Scy- 



phozoa (Gr. O-KV^O?, a saucer). These animals are 



the larger and better known jelly-fish. They are to 



some extent intermediate in character between the Hydrozoa and 



the Actinozoa. Like the latter their genital cells are developed 



from endoderm, and in the larval condition there are mesenteries, 



but they do not possess a stomodaeuin. 



A common British species, Aurelia aurita, is in summer often 

 cast by thousands on the southern shores of Great Britain. Viewed 

 from the outside it very much resembles the medusoid persons of 

 the Hydromedusae. Like them it possesses a swimming bell with 

 a circle of tentacles at the margin. There is also a prominent oral 

 cone or manubrium. This however does not bear real tentacles, but 

 the four corners of the rectangular mouth are drawn out into long 

 frilled lips (2, Fig. 33), along the inner sides of which are open 

 grooves leading into the gullet. Perhaps the most marked difference 

 is that the reproductive organs are here, as in the Anemones, 

 swellings 'of the wall of the stomach : the eggs and spermatozoa are 

 shed into the coelenteron and escape by the mouth. The generative 

 organs have the shape of four semicircular ridges, and along the 

 inner side of each of these there is a row of filaments composed of 

 cells somewhat similar to the cells on the edges of the mesenteries 

 in the anemones (11, Fig. 33). Nothing like these gastral fila- 

 ments, as they are called, is found in the Hydromedusae. There is, 



