28 BRITISH FOSSIL CORALS. 



Gemmation from the wall — the lateral form — may occur at the top so as to affect the 

 calicular margin, and at any place between this and the base. The gemmation may be 

 solitary, alternate, M'horled, numerous, or irregular ; and the parent may or may not grow 

 after the development of the buds.^ 



The genera Claclocora, Solenastraa, Oculiiia, Lophohelia, ^[adrepora, HeliasircBa, 

 Sti/Ioccenia, Stylina, Asfrocoenia, Slephanocania, &c., furnish examples of lateral and 

 marginal gemmation. 



The basilar gemmation is especially to be observed in the genera Mhizangia, Astrangia, 

 Plii/llanffia, and other Astrangiacea. 



Fissiparotis growth. — Many corals increase in dimension and become caespitose, 

 gyrate, laminar, or massive, by a repetition of a fissiparous process in the calice or calices. 

 The general nature of this method of calicular division and subsequent growth may be 

 seen in Plate IV, figs. 12, 13. The calice is fairly bisected through the columella or 

 columellary space by the growth of two or more opposite septa, and the wall appears to 

 curve inwards, whilst the parts on either side grow independently and separate with 

 varying rapidity. The process may be more or less speedily repeated in the new calices, 

 and as they separate and grow npwards they may or may not be enveloped in 

 coenenchyma. 



Very differently shaped corals thus result. 



The genus Dichocoeiiia offers examples of massive corals where there is fissiparous 

 growth and much coenenchyma. The genus Favia has its fissiparous individuals in close 

 contact, and the species of Thecosmilia yield long, dendroid, and caespitose forms. 



Serial groioth} — Corals of the genus Dijihria, LathiKScmdra, Bhipldogyra, Pcdinia, 

 Teleiophyllia, Thysanus, Manicina, &c., have either faint traces of calices running laterally 

 into each other, or else the septa follow each other in a longer or shorter series, which is 

 sometimes straight, at others twisted. The occurrence of coenenchyma, and the particular 

 manner in which the " series" may be joined laterally, determine the shape of the corallum. 

 In the LathnceandrcB the faint traces of calices may be seen. In Diploria and Mmandrind' 

 the septa are in series, and form a massive coral ; whilst in the TdeiophyUi(B and Tliysani,*" 

 where there is a long series, the corallum is simple and pedicillate. 



Gemmation occurs both in fissiparous and serial corallites. 



v.— PHYSIOLOGY. 



The ovules of corals are projected from the visceral cavity through the pyloric con- 

 striction, the stomach, and the mouth, by the contraction of the tissues of the disc; and the 

 cilia of the cavities assist the transit. Cilia cover the small ovule and move it onwards 



' Plate IV, fig. 16, 17. - Plate IV, fig. 14. = Plate IV, fig. 15. 



♦ Plate IV, fig. 14. 



