THE LOWER FORMS OF LIFE. 



Ill 



CHAPTER VII. 

 CORAL. 



THE Actinozoa are divided into four orders. The first of these, the 

 Zoantharia, comprises the sea-anemones, including the small variety 

 which builds coral reefs ; the second, called Alcyonaria (because 

 the typical species was at one time presumed to be the hardened 

 foam of the sea wherewith halcyons build their nests), is repre- 

 sented by the polyp which forms the well-known red Coral of 

 commerce, the curious horny Coral known as the " Sea-Fan" or " Sea- 

 Pen, " and still more popularly by the leather-hardened foam-looking 

 masses which the sea-side rambler recognises as " Cow Paps " or 

 " Dead Men's Fingers ;" the third order is constituted of an extinct 

 fossil family of Coral builders, the Eugosa ; and the fourth and 

 most highly organised is called, by reason of the serrated or comb- 

 like appearance of some of the species, the Ctenophora, all the species 

 of which are oceanic and free. 



I will say a few words about the order Alcyonaria first, because 

 the species which form it build up their Coral skeletons in a different 

 manner to that which is adopted by the Zoantharia. There are, in 

 fact, two great plans upon which Coral is formed, and I will shortly 

 illustrate both of them. 



Fig. 147. Sclero-basic. 



Fig 148. Fig. 149. Sclero-dermic. 



Fig. 147. a, Coral secreted by outer skin of the base of the polyp, and extending from 



below upwards. 



Fig. 148.-Coral formed by this means as seen in red Coral of commerce. 

 Fig. 149. a, Coral secreted from the inner skin, and extending from without inwards, as in 



reef-building Corals. 



The figures 147 and 149 represent two ideal or diagrammatic 

 longitudinal sections of Actinozoons, the former being one of the 

 Alcyonaria, and the latter one of the Zoantharia. 



