TRIBE I.— ASTR^EACEA. 



All the members of this Tribe with which we are fami- 

 liar on the European shores are simple, and destitute of 

 a corallum. But when those of all seas are taken into con- 

 sideration, we find that the majority are compound and 

 coralligenous. The increase of these is effected by the 

 budding forth of new polypes from the single primary 

 polype ; and it is in the manner of this gemmation that 

 the tribe Astraacea differs from the Caryopliylliacea. In 

 the former, increase invariably takes place by the extension 

 of the summit, and not of the side or base. The process of 

 widening, in budding polypes, may be confined to the parts 

 exterior to the disk and visceral cavity below, or the disk 

 and cavity may continuously enlarge ; in the latter case, 

 the buds open in the disks, the process of budding being 

 the cause of their enlargement (Dana). 



The greater part of the Astrceacea increase by disk-buds, 

 and spontaneous subdivision ; the disk of the polype, and 

 the cell of the corallum, gradually widening by growth, 

 and finally separating into two portions, which become in- 

 dependent. A few only widen exteriorly to the disk, or in 

 the interstitial spaces between the cells of aggregate corals 

 (Dana). 



The polypes in both this and the following tribe are 

 many-tentacled ; but, while this character distinguishes 

 them from the two other tribes, it is of no assistance in 

 discriminating those species with which we have to do. 

 Moreover, as our Astraacea are all simple, it is difficult to 

 apply the rule derived from the manner of gemmation. 

 The spontaneous fission of some species, however, as 

 Actinoldba diantlins, partially, and Anthea cereus completely, 

 may help us to assign their affinities ; and their general 

 resemblance, inter se, and that of the whole to the polypes 

 of the coralligenous Astraacea, leave little room for un- 

 certainty. 



