CORAL-MAKING ACTINOID POLYPS. 59 



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 masandrine furrows are made, some kinds of 

 which are popularly called Brain coral, and pertain to the 

 Meandrina family (figure on page 65). 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 re- 

 quire for the explanation of their origin only the few principles 

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

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

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

 drophyllia, with its summit polyp (figures p. 50, 51), or that of 

 the Porites, with its terminal budding clusters (p. 53) ; or the 

 rising, massive dome of the Astraea and Maeandrina (pp. 57, 

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

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

 ing stem bearing at top the single polyp that originated it, or 



