CLASS 1 ANTHOZOA 71 



(Knflii'';ili,i). In many <;,>> the peripheral edges of the septa become thickni.-d 

 and laterally fu.-ed tn form a spurious theca (Psetnl<>l/i' </>" ); and occasionally 

 the dissepiments lyin-- in a certain zone become united BO as to form an inner 

 wall within the true thcca. The rj,tth<;;i is a usually smooth, sometimes 

 corrugated, superficial calcareous investment, which, according to Koch, is 

 merely a prolongation of the liasd plate, and is secreted by the outer surface 

 of the ectoderm, which is reflected over the top of the corallum. The epitheca 

 is deposited either directly upon the theca, or, when the septa are produced 

 outwards so as to form exothecal lamellae or ribs (W^-), the theca and epitheca 

 are separated. Exothecal lamellae, not corresponding in position to the septa, 

 are called y/>r//,/// ( v,s/W or rut/tic. 



Sexual reproduction is comparatively rare among Anthozoans. Following 

 fertilisation and segmentation of the ova, ciliated larvae are born, which swim 

 a 1 >out for a time, become fixed, and develop into simple polyp individuals. 

 Asexual reproduction by gemmation or fission is much more common. The 

 individuals produced in this way remain connected with one another and with 

 the parent animal, forming polyp stocks or colonies of exceedingly various 

 forms and sizes. 



New corallites are produced either within or without the calice of the 

 parent polvp. In extra- calicinal gemmation, the buds are thrown out either from 

 the sides of the polyp (lateral ija iunation\ or are formed in the common 

 calcareous matrix which unites the various corallites of a colony (coerienchymal 

 and f<>4l ffemniatiori). In both cases the new corallites may diverge from one 

 another, being attached to the parent corallum only at the base, or they may 

 grow up closely opposed to the latter and to one another, so that the thecae 

 are in contact on all sides. In this way, branched, dendroid, or massive and 

 knob-like ( " astraeif orm ") compound coralla are formed. A less common 

 mode of increase is by basal or stolonal gemmation. In this process the Avail of 

 the original polyp sends out creeping prolongations (stolons) or basal expansions, 

 out of which new corallites arise. In calidnal gemmation buds are produced 

 within the calice of the parent corallite, according to one or the other of the 

 following methods : Either certain particular septa become enlarged and pro- 

 duced so as finally to enclose a new calicinal disk (septal gemmation) ; or tabulae 

 are produced upwards in the form of pockets, from which neAv corallites are 

 developed (tiilnilur ijciniiuitin). In both septal and tabular gemmation, a portion 

 of the parent corallite including a part of the original Avail is concerned in the 

 formation of buds; while the septa or modified tabulae are converted into 

 portions of the new thecae, from which neAv septa then begin to grow inwards 

 toward the centre. 



A peculiar kind of calicinal gemmation is that known as rejuvenescence. In 

 this method only one bud is formed within the parent calice, but it enlarges 

 until it completely fills the latter. By the indefinite repetition of this process, a 

 corallum is formed, consisting of a succession of cups placed one within the other, 

 of which only the youngest and uppermost is occupied by the living animal. 



The beginning of reproduction by fission is marked by an elongation or 

 distortion of the parent calice, accompanied by the contraction of the Avail at 

 pposite points along the margin. The constriction may proceed until it 

 divides the oral disk into tAvo halves ; or tAvo opposite septa may unite to form 

 a new theca. By this method, branching, massive, or astraeiform colonies are 

 produced, Avhich do not differ essentially from those formed by budding. 



