8 
TRIBE L— ASTR^ACEA. 
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 Aslrc&acea differs from the Caryoj^liylliacea. 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 Astrcecicea 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 Astraeacea are all simple, it is difficult to 
apply the rule derived from the manner of gemmation. 
The spontaneous fission of some species, however, as 
Actinoloba diantlius, partially, Antliea cereus completely, 
may help us to assign their affinities ; and their general 
resemblanee, inter se, and that of the whole to the polypes 
of the coralligenous Astraacea, leave little room for un- 
certainty. 
