ORDERACTINOIDEA. gl 



existence at the developement of the young, which thus starts from it. 

 In figure -^Sr, three polyps proceed together from the centre of the 

 parent; and, in^,'l;he new polyps sprout just exterior to the centre. 

 Nothing in the history of corals seems more remarkable than this 

 strange mode of reproduction. Yet the fact, that the Tubularise and 

 some Sertularidas, drop their flowers, and renew them at intervals, as 

 explained in § 18, appears to be quite analogous. In these Cyathophyl- 

 lidsB, the parent, at the bvidding period, appears to lose its tentacles 

 and disk, as in the Tubularise, which may disappear by the with- 

 drawal of nutriment, needed for the new developements in progress ; 

 life remains only about the centre, and from this part, the germ rises 

 and the young is produced, the parent surrendering its existence at the 

 birth of its successor, or soon afterward. In the second of the above 

 figures, three young proceed from the ashes of the parent, instead of one. 

 The third figure shows that many germs may exist and grow out from 

 different parts of the summit in the same course of changes. This 

 process is closely related to the interrupted mode of increase ex- 

 plained in \ 62. 



82. From the preceding discussions, we perceive that glomerate, 

 foliaceous, and ramose forms may occur under each mode of budding 

 and growth. Yet glomerate zoophytes are most common among the 

 Astrisacea, and here alone they assume hemispherical or globular 

 shapes of perfect symmetry; branching and foliaceous species are 

 few in number in this tribe, and are distinguished by having the 

 buds open a little below the apex, as well as by their lamello-striate 

 surface. The Madreporacea and Caryophyllacea present occasional 

 glomerate forms, usually of rude shape ; but generally they are ramose, 

 and often foliaceous. The branches are not lamello-striate, and the 

 buds open at the extreme apex or margin. The Alcyonaria may pro- 

 duce branching coralla through their foot-secretions, and occasional 

 segregate forms, like the Tubipores ; but none are yet known which 

 are properly massive. 



Both massive, foliate, and ramose species often belong to the same 

 genus, and in some instances, as before stated, a coral is thin foliaceous 

 in one part, and glomerate in another, or covered with rudimentary 

 branches. 



In conclusion, the principal distinctions, as to modes of growth 

 among zoophytes, are as follows : 



1. Acrogenous, when polyps grow upward indefinitely, death taking 

 place at a corresponding rate below ; and the reverse, non-acrogenous. 



21 



