4 88 
CCELENTERA TES. 
egg-ca 
medusae 
more than two kinds of individuals; namely, the nutritive individuals, dis¬ 
tinguished by their long tentacles, mouths, and digestive cavities; and the 
reproductive individuals, male or female. These latter have no mouths, and are 
supplied with food through the system of canals running to them from the 
nutritive individuals. These reproductive individuals, instead of tentacles, carry 
at their tips a circle of stinging- 
batteries for the protection of 
their eggs, which are enclosed in 
capsules clustered together round 
the stalk a little way below the 
tips. The ciliated larvae emerg¬ 
ing from the eggs swim away, 
and eventually become attached 
and found new colonies. The 
in no way recall 
but all medusae which 
pass through a polyp-like inter¬ 
mediate stage also pass through 
the simple capsule stage. 
Two more of the Hydroid 
stocks are worth mention, since 
they secrete masses of carbonate 
of lime out of which the animals 
protrude like corals, which indeed 
they were thought to be. This 
error was made because only the 
massive skeletons of the Hydro- 
corallia—as they are called—and 
not the living animals were 
known. Instead of the horny, 
often delicately branching in¬ 
tegumentary skeleton usually 
found in the Hydroid polyp 
stock, that of the Hydrocorallia 
contains ninety-seven per cent, 
of carbonate of lime, and forms 
rough, solid-looking masses, with 
lobed processes or bosses like 
those figured on p. 490, or else 
( Stylasteridoe ) branches, like the precious coral of commerce. The whole surface 
can be seen even with the naked eye, but still better with a lens, to be covered 
with small pore-like apertures. Closer examination shows that these are of two 
sizes, a larger central pore being surrounded by an irregular circle of from five 
to eight smaller ones. The mass of the colony is traversed by an irregular 
system of numerous branching canals of different sizes. In vertical section, 
indistinct layers can be seen running almost parallel with the outer surface. 
group of a femalf. stock of Hydractinia echinata. 
a, Nutritive individuals ; b, Female individuals. (Enlarged.) 
