38 CORALS AND CORAL LSLANDS. 



this mode of branching. In the left-hand polyp there are 

 already two mouths, and the work of subdivision is consequently 

 begun ; while in those to the right, which have a single mouth, 

 the subdivision has just been completed, and also the forking of 

 the old branch. Thus spontaneous fission goes forward, and 

 branches accordingly multiply. By this method some of the 

 most magnificent clumps of coral zoophytes found in tropical 

 seas have been, and are being, developed each from a single 

 germ. Many of them have the perfect hemispherical symmetry 

 of the solid Astraeas. 



Sometimes, when a new mouth forms in an enlarging disk, 

 there is not at once a separation of the two, but the disk con- 

 tinues to enlarge in one direction and another, and then 

 another mouth opens, and so on until a string of mouths exists 

 in one elongated disk ; and finally, a separation occurs, but 

 only to commence or carry forward another long series. In 

 this way the corals with meandrine furrows are made, some 

 kinds of ^\^hich are popularly called " Brain coral," and pertain 

 to the Meandrina family (figure on page 4-4). The same may 

 take place in the ramose corals, and so make flat branches, 

 each with a long sinuous line of polyp mouths at top. In all 

 such species the tentacles stand in a line either side of the 

 line of mouths. 



By the simple methods here explained all of the various 

 forms of Actinoid zoophytes have been produced ; and, equally 

 so, those of the Alcyonoids described beyond. The tree, 

 shrub, clusters of coral leaves, hemispheres, and coral net-work 

 require for the explanation of their origin only the few princi- 

 ples which have been mentioned. The germ-polyp, growing 

 upward and more or less outward, and budding as it grows, 

 makes thus the rising stem — that of the Madrepore or Dendro- 

 phyllia, with its summit polyp (figures p. 29, 31), or that of the 

 Pontes, with its terminal budding clusters (p. 2iZ) 'i *^'* the 

 rising, massive dome of the Astrsea and Mcneandrina (pp. 37, 

 44), in case budding is symmetrical in all directions ; — or, if 

 growth in the germ-polyp is upward exclusively, it forms a 

 rising stem bearing at top the single polyp that originated it, 



