202 ZOOPHYTES. 



plate 10, the lamellse of the stars may be traced into the intervening 

 septum, (except when it is very thin,) and the limits of the star may 

 often be seen to be produced by a thickening of the lamellse till they 

 coalesce laterally ; and when the septum is broad, the lamellae often 

 narrow again after this coalescence, leaving cellules between in the 

 middle of the septum. In some species these cellules are linear or 

 > -shaped, and in others they are polygonal and in two series. Occa- 

 sionally they are entirely wanting, from the compactness of the coral- 

 lum : yet even in these cases the lamellse composing the septum may 

 be usually distinguished. 



The greater part of Astrseas increase by disk buds, and sponta- 

 neous subdivision; the disk of the polyp, and the cell of the corallum, 

 gradually widening by growth, and finally separating into two por- 

 tions, which become independent ( 79). A few widen only exterior 

 to the disk or in the interstices, instead of the cells, and buds in this 

 case open in the interstitial spaces between three or four cells (& 76 d) 

 Those species which increase in the latter way, are in general dis- . 

 tinguished by having 'the calicles more distant and prominent than 

 the others, or with wider and more concave interstices. The process 

 as it goes on in the Astrcea argus, may be easily studied. The lamella? 

 which intersect the septum, extending from either side half way across 

 it, become separated a little at the middle of the septum, in conse- 

 quence of this widening ; and thus, in the medial point between three 

 cells, these lamellse actually begin to radiate around an open space. 

 This is the commencement of a new star, and a new polyp ; the bud 

 soon after opens. There are some species, the A. stellulata, stettigera, 

 intersepta, in which increase takes place both by these interstitial buds 

 and by the dichastic process. 



Though the cells of Astrseas are usually simple, and contain only a 

 single polyp mouth, except during the process of subdivision, yet in a 

 few species they become elongated, so as to contain three or four 

 mouths, and thus approach the Meandrinas ; and in the same speci- 

 men, simple and oblong linear cells are intermingled. The A. defor- 

 mis is an example, and were it not that the simple cells are the most 

 numerous, it should be placed near the Meandrina dedalea, and M. 

 spongiosa. The M. spongiosa appears to be often a true Astraea in its 

 characters, and the A. varia closely resembles some of its varieties. 



These corals are confined, with rare exceptions, to the coral-reef 

 seas, and contribute largely to the construction of reefs, both in the 

 Pacific and in the East and West Indies. 



