ANTHOZOA ZOANTHARIA. 741 



par aria Perforata, or by their gastric cavities, as in Coeloria, Maeandrina,&z., 

 corals in which they are disposed in linear series. 



Asexual reproduction has been observed in few of the non-colonial 

 Actiniaria. Part of the limbus may separate off in some Hexactiniae and 

 develope into a new zooid : such a process is known as scissiparity (p. 241). 

 Fission occurs commonly in Ammonia sulcata (^ Anthea Cereus\ and may 

 be the cause of the occurrence of twin individuals in Actiniloba dianthus, 

 &c. The colonial forms increase in various ways which have been classi- 

 fied by von Koch under the two heads of internal and external gemma- 

 tion. In the former, the young calycle originates with the parental, and 

 is derived partly or entirely from it : in the latter, it is external to it 

 altogether. Internal gemmation occurs (i) as fission-budding, in which 

 the original calycle is constricted into two parts, e. g. in Mussa ; (2) as 

 septal budding, seen in the Silurian Stauria and its allies, where the 

 so-called primary septa become in part the walls of the young calycles ; 

 (3) tabular budding, in which the young calyx is produced from the 

 parental, but is completed by the development of a pocket-shaped floor or 

 wall. As to external gemmation, the bud is either formed (4) from the 

 wall of the parental theca, and adheres closely to it as in Favosites, which is 

 probably, however, an Alcyonarian ; (5) in coenosarcal budding from the 

 tube of the coenosarc, e. g. Madrepora, or of the coenenchyma (?), e. g. 

 Rhodopsammia ; or (6) in stoloniferous budding, from a stolon, as occurs in 

 some extinct operculate Corals 1 . Individuals are sometimes found with a 

 new but smaller calycle symmetrically formed within an old calycle with 

 which it corresponds completely. This is termed * rejuvenescence ' by von 

 Koch. In Fungia there is a small fixed stock simple (or branched ?) from 

 which the apical zooid-portion is detached, a new zooid arising by gem- 

 mation from the pedicle. The process may be repeated 3-4 times. The 

 detached zooid is i^in. in diameter and shows a scar of detachment which 

 disappears during subsequent growth (Moseley) 2 . 



1 Of these various modes, (i) and (2) are often termed simply 'fission,' and (3) 'calycular 

 gemmation/ very common in the extinct Rugosa. Fission may be quite imperfect ; e. g. Dana states 

 that the long lines of the Maeandrine corals are due to the lengthening out of the peristome and the 

 formation of a series of mouths, the elongated and many-mouthed disc being fringed by a line of 

 tentacles on either side. (4) Is termed by von Koch ' Zwischenknospung,' and does not occur in 

 any living coral.. (5) Is a very usual form, and is commonly spoken of as 'parietal gemmation.' 

 As to (6) it is, strictly speaking, only a mode of (5), inasmuch as every stolon contains coenosarcal 

 tubes. There can be no doubt that the stolons of extinct Anthozoa contained similar extensions of 

 the coelenteron. According to Martin Duncan, the epithecal roots of the living Rhizotrochus are 

 hollow and open into the calycle. 



2 The Fungia stock is probably never branched, but two or three stocks may grow close upon 

 one another. Stutchbury states that the pedicle of the stock becomes bare of soft tissues when 

 the terminal part is detached. The mode in which the second zooid buds from the stock is not 

 known. Semper mentions in his paper (Z. W. Z. xxii.) several interesting facts relative to the 

 asexual multiplication of Madrepores. Blastotrochus nutrix is simple, properly speaking, but from 

 the bare sides of the theca originate buds which drop off. The pedicle of the bud left in situ forms 



