ORDER ACTINOIDEA. 15 
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. 
6. The following figure of a foliaceous Echinopora illustrates the 
process where the growth is a simple marginal prolongation not ex- 
tending to the disks. 
Fig. 33. 
Echinopora. 
By the prolate mode of growth, the polyps gradually extend out- 
ward, and new buds open, from time to time, a short distance from 
the edge, and have no connexion at base with the preceding polyps. 
The corals of these species have the upper surface striated, indicating 
the presence of visceral lamelle within the extending part, from 
which buds may proceed. The contrast between this and the Gem- 
mipora (j 66), in each of the above particulars, is made apparent by 
a simple comparison of the figures; for in the latter, the buds, besides 
opening at the very margin, may be traced within to a preceding 
polyp, from which each is a lateral shoof: and, moreover, the surface 
is not striated. : 
c. The above Echinopora, and other foliaceous corals among the 
Astreide, are examples of prolate growth without the acrogenous. 
But the massive Astreas are produced by the united action of these 
two modes of growth, and their hemispherical 
forms result from the perfect regularity and 
symmetry in the process of budding. 
d. Several species of Astras afford examples AS 
of the mode of gemmation, illustrated in the Rul pe 
Echinopora, among which is the Astrea argus. 7#i%3 
While the margin of the hemisphere is extend- 
ing by the multiplication of buds, precisely @#* 
similar to that above, the whole surface is also gra- 2a 
dually enlarging by a widening of the intervals epee) stens: 
between the polyp-disks. But this widening is kept within limits by 
the appearance of new buds in these intervals when they begin to exceed 
