COELENTERATA 57 
of lime are built up, simulating some of the true corals. 
Certain tubular spaces are left for the accommodation of the 
hydranths, which can be withdrawn into them. The hydranths 
are colonial, and of two kinds : gastrozoids, provided with mouths, 
which are the nutritive persons of the colony ; and dactylozoids, 
elongated mouthless persons well armed with nematocysts. 
The order is divided into two familes: (i.) the MILLE- 
PORIDAE and (11.) the STYLASTERIDAE. 
(i.) THE MILLeporIpAE.— This family may have an arborescent 
or branching skeleton, consisting of an outer living part 
which surrounds an inner and older dead part. The 
younger parts of the pores, in which the living hydranths 
are found, are separated from the older ones, wherein 
their predecessors lived, by horizontal partitions known as 
tabulae. The colonies are hermaphrodite. 
(il.) THE STYLASTERIDAE.— These are always arborescent, never 
encrusting, and their colonies are unisexual. 
The hydranths may be scattered irregularly, but more 
usually the gastrozoids are surrounded by a regular circle of 
Fic. 41.—Longitudinal median section 
through a Stylasterid. After Hickson. 
1. Gastrozoid. 
2. Dactylozoid. 
3. Style. 
4. Coenosarcal canals. 
Or 
Coenosare, calcareous, 
6. Mouth. 
Tentacle. 
“I 
dactylozoids. The gastrozoid (Fig. 41) is usually provided 
with tentacles, but in some of the STYLASTERIDAE these are 
wanting. The dactylozoids are long tentacular structures with 
