7 o6 



COELENTERA TA II. CNIDARIA . 



than the rim. The young, as a rule, bud from the under surface of the 

 parent, then drop off, and lie loosely on the rock or sea-bottom. A branched 

 form is known in which young Fungia drop from the tips of branches. 



This branching condition, which is exceptional in the Mushroom corals, 

 is the rule in nearly all other corals. By division or budding of various 

 kinds an endless variety of colonies are produced. Sometimes, as among 



the Zoophytes, the polyps build up 

 branched frameworks, from which 

 at intervals they protrude, like 

 flowers from a branched stalk. 

 The form of such colonies depends 

 upon the intervals separating the 

 polyps, and the angle at which 

 they branch out from the parent 

 individuals. In Fig. 14, in the 

 coral on the left, the polyps are far 

 apart, in that on the right the 

 budding is frequent and the polyps 

 crowded. In this latter case the 

 skeleton is penetrated in all direc- 

 tions with canals which, for a cer- 

 tain distance below the surface, 

 carry food juice from polyp to 

 polyp. The Madrepores, of which 

 the coral to the right of Fig. 14 is 

 an example, are amongst the most 

 important builders of coral reefs 

 and islands. Other coral colonies form waving plates, often beautifully 

 frilled at the edges, the polyps usually projecting from the upper surface of 

 the plate. The variety in form and structure of coral colonies is, indeed, 

 almost endless. 



Entirely different coral forms are produced by polyps which, instead of 

 budding, simply divide into two or more new individuals. In Fig. 15 we 



have a hemispherical mass, the surface 

 of which is thickly set with star-like 

 polyps ; some are seen expanded, with 

 the slit-like mouths in the centre of the 

 disc, others are in a retracted condition. 

 The star-like shape of the polyps in 

 this kind of coral has obtained for it the 

 name of star-coral. On such a mass a 

 larger polyp is often found which has 

 two mouths instead of one ; a row of 

 tentacles forms between the two 

 mouths, this row then breaks up 

 into two, and two polyps are seen on 

 the surface where only one was before. 

 In this case we have complete division of the individuals, for, while these 

 outer changes have been going on, corresponding changes have been taking 

 place below the surface, resulting in a more or less complete division 

 of the original animal into two. In these colonies, the whole hemispherical 

 mass, which may grow to an enormous size, is built up layer after layer, the 



Fiff. 14.-CORAL COLONS. 

 Dendrosoma. Madrepora. 



Fig. 15. THE STAR CORAI/ (Astrcea). 



