142 PHYLUM C@LENTERA. 
The sea-anemones and their numerous allies may be 
regarded as bearing a relation to the jelly-fish, somewhat 
similar to that which the hydroid polyps bear to the 
swimming-bells (Fig. 65). They are, however, much more 
complicated in structure than the hydroids. Solitary forms 
are much commoner than in the hydroids, but the colonial 
type is nevertheless very frequent. The colonies may be 
supported by an organic framework only, but very commonly: 
there is a tendency to accumulate lime in the tissues, which 
results in the formation of “corals.” It should be noted, 
however, that various quite distinct polypoid types may 
form “corals.” Thus, while the most important reef-building 
corals are included in the Anthozoa, the Millepore-corals 
are hydroids. 
Finally, as the corals are predominantly passive, so there 
is a climax of activity in the Ctenophores, which move by 
cilia united into combs, and often shine with that ‘ phos- 
phorescence” which is an expression of the intensity of life 
in many active animals. 
As to diet, many of the larger forms, ¢.g. sea-anemones 
and jelly-fish, are able to engulf booty of considerable size ; 
the active Ctenophores are carnivorous, attaching them- 
selves by adhesive cells to one another, or to other small 
animals; but most Ccelentera feed on small organisms, in 
seizing and killing which the tentacles and stinging cells 
are actively used. 
Stinging cells or cnidoblasts are so characteristic of Ccelentera that 
they deserve particular notice. They occur, in all Coelentera except 
the Ctenophores, and even there they have been detected in Zuchlora 
rubra. They also occur in some Turbellarian worms, and in the 
papillz of A®olid nudibranchs amongst molluscs; but it has been 
shown that these animals obtain their nematocysts from the Ccelentera 
on which they feed. Each cnidoblast contains a capsule or nemato- 
cyst, which encloses a coiled lasso lying in an irritant gelatinous 
substance. The nematocyst fills most of the cell, but there is a nucleus, 
etc., besides. At the distal end there may be a trigger-like cnidocil or 
a fringe of bristles, etc. At the proximal end there may be fixing 
processes. In some Anthozoa the coiled lasso is simply ruptured out, 
but in most cases it is evaginated. The basal part of the lasso is 
often stronger than the rest, and may bear stilets; spirally arranged 
roughnesses and bristles are also frequent on the thread itself. The 
explosion of the cnidoblast is believed to be due to an entrance of 
water, which causes the gelatinous substance to swell up. According 
to others, the cnidoblast contracts as a whole. The action of the 
