CORALS. 



5U 



We conclude our description of these eight-rayed corals with the organ-pipe 

 corals (Tubiporidcv), a family consisting of the one genus Tubvpora. the members 

 of which are neither numerous nor varied. 

 The individuals resemble in form, in the 

 number of their delicate tentacles and in 

 their soft anterior body, the other living 

 members of the order. In the structure of 

 their skeleton they are, however, unique 

 among extant corals, and recall certain 

 extinct forms. Each individual secretes 

 a smooth-walled tube, without calcification 

 of the vertical septa. These tubes, which, 

 like the pipes of an organ, stand almost 

 parallel, are united to form a stock by 

 means of transverse platforms. These 

 latter do not, however, correspond with 



RED CORAL. 



1, Part of a stock with retracted polyps, two have 

 been opened (magnified) ; B, With polyps more 

 or less extended ; a larva (a) seen in the act of 

 emerging through the mouth of the uppermost 

 polyp. 



organ-pipe coral, Tubipora (nat. size). 



a, Starting points of new individuals 

 (nat. size.) 



the inner transverse parti- 

 tions (tabvlce), by means of 

 which the upper living part 

 of the tube is from time to time cut oft' from the dead part below. The 

 transverse platforms are neither regularly parallel nor continuous ; neverthe- 

 less they do indicate in a general way stages of growth. They are very richly 

 provided with nutritive canals, and are of special importance for the whole stock, 

 inasmuch as the young individuals bud out from their surfaces. As the longer 

 tubes grow, the intervals between them increase, and as soon as there is room 

 enough for a new polyp, one buds out from the platform. Division of the 

 individuals or formation of buds from the tubes themselves does lAt take place in 

 this family. 



Coral-Reefs Having described a few typical corals, and explained their 



and islands, general structure and characters, some mention must be made of the 



importance of these creatures in the economy of nature. Whereas most forms of 



