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in which two or more distinct layers entered into the composition of the 
body substance. In the class Hydrozoa there was no intervening space 
between these two layers, but in the class Actinozoa such a space existed, 
and was filled with the reproductive and other organs. The universal 
distribution of the Coelenterata was then alluded to, as well as the fact that 
they were nearly all marine, and that the formation of all coral was due to 
certain members of this sub-kingdom. 
The Actinia, or sea-anemone, might be taken as the type of the second 
division, Actinozoa, although it was by no means the most highly organized 
member of the class, still all its members presented the same structural 
peculiarities. Its external appearance was familiar to most persons ; in its 
contracted state it might be likened to a more or less depressed cone, 
rounded above, the base rather spreading ; when expanded it might be 
described as a fleshy column or cylinder usually attached by the base, the 
opposite end being surmounted by many tentacles disposed in two or more 
concentric alternative circles, in the centre of which was placed the mouth. 
From several causes it was enabled to effect some remarkable changes in 
its form and appearance. Its locomotion was very slow, being performed 
chiefly by contractions of its base. Some species changed their colour 
when living in pools, &c, periodically uncovered by the tide, to correspond 
with the colour of the rock, or sand, to which they were attached. 
Externally the body was usually soft and fleshy, sometimes leathery, and 
frequently covered with wart- like papillae, which secreted a viscid fluid, 
and were also powerful suckers. In the mature animal there were more 
than two distinct tissues, and the principal thickness of the body wall was 
made up of two sets of muscles, the outer of which was disposed circu- 
larly, aud the inner longitudinally ; these fibres, however, were not striated, 
as normal muscular fibre was. The ectoderm was divided into two layers, 
between which the thread-cells were found, called the dermal and epithelial 
layers, and immediately underneath the former were found the pigment 
cells. The stomach was simply an invagination of the body wall, aud 
possessed essentially the same structure. The tentacles were hollow, and 
frequently perforated at the extremities, the openings being closed by a 
sort of sphincter muscle, and the whole having a free communication with 
the interseptal chambers ; their development in the young animal took 
place in a series of concentric circles, each of which, reckoning from within 
outwards, contained, the second only excepted, twice the number of 
tentacles of its predecessor. In some Actinice, outside the tentacles, were 
little wartlike blue bodies, supposed by some observers to be rudimentary 
eyes ; the author, however, did not regard them as such, and found them 
to contain an enormous number of cnidae, and amceboid-like particles of 
sarcode. The mouth was slightly oval in form, and provided with a pair 
of tubercles (gonidia) whence ran two canals as far as the termination of 
the stomach, which was a short tube somewhat flattened, hanging freely in 
the centre of the body, capable of distension, as well as of being closed at 
