CORALS. 
5°7 
in which the coral-stocks grow, we can only select a few types. In Dendroplujllia , 
as shown in the illustration, we have a tree-like growth; each polyp secreting a 
solid pedestal for itself, 
and living in a depres¬ 
sion in the top. This 
is shown in the section 
B. Into this depres¬ 
sion the soft animal 
a branchixg coral, Dendrophyllia. 
A, Terminal branch of a stock (uat. size); B, Longitudinal section of a single polyp (magnified). 
can withdraw at the approach of danger, drawing all its tentacles (which also 
contract) down to a. The space occupied by the animal is not very roomy at 
the best, and it is further limited both by a great columella cl, rising up in its 
interior, and by the solid septa l> projecting into it 
all round. It must not be forgotten that these parts 
are not in the animal but outside of it, and as they 
are secreted they push the skin up and never pene¬ 
trate into the tissues themselves. These polyps bud 
at intervals, the apical polyp most frequently; and 
the result is a simple branched stock, as seen. 
A different kind of stock is developed when the 
polyps produce many buds, as in the madrepores. 
In these delicate stocks, selected polyps spring up 
above the rest, and their sides become covered with 
small buds. Space 
would obviously 
not permit all 
these small buds 
to bud again in 
the same manner. 
A few favoured 
ones, however, 
which have suffi¬ 
cient room next 
spring out and 
a madrepore coral (Madrepora verrucosa). become CON el t'd 
lu flic section B the canals which connect the polyps through the stony skeleton are seen, again with small 
