ZOOPHYTES 473 



an extent is this carried, that if an individual is cut into several 

 pieces, each of them becomes a fresh Hydra. Powers of this kind 

 are common among lower animals, and, as might be expected, are 

 greatest where the body is but little specialized, as in the case now 

 under consideration. Another case was mentioned when dealing 

 with the Star-Fish (p. 454). The absence of specialization in Hydra 

 is not so great, however, as supposed by the older zoologists, who 

 imagined that the animal was so little discomposed when turned 

 inside out that it lived on with the functions of the layers reversed. 

 Zoophytes are conveniently divided into the following three 

 classes: i. Sea-Flowers (Anthozoa or Actinozoa); 2. Hydroids 

 (Hydrozoa); and 3. Comb Jelly-Fish (Ctenophora), 



CLASS I. SEA-FLOWERS (ANTHOZOA or ACTINOZOA) 



The brilliantly-coloured Sea- Anemones, Corals, Sea- Pens, and 

 the like, which are grouped together in this class, justify its name 

 (Gk. anthos, a flower; zoon, an animal), for, when expanded, they 

 look not unlike chrysanthemums or double dahlias, to the indi- 

 vidual florets of which the numerous tentacles bear a certain 

 resemblance. Many of them are colonial, while others live singly, 

 and of these we may take the common Beadlet (Actinia mesem- 

 bryanthemum) as an example (compare fig. 290). It is abundant 

 on rocks between tide-marks all round our coasts, looking, when 

 expanded, like a scarlet flower, but shrinking to a rounded jelly- 

 like mass when contracted. In the former condition, it may be 

 compared to a short broad Hydra, but the mouth is in the centre 

 of a wide disc, and is surrounded by several rows of comparatively 

 short pointed tentacles. There are, however, important differences 

 in structure. The mouth leads, not into a widely -continuous 

 digestive cavity, but into a tubular gullet, which hangs down within 

 the body, and ends abruptly below. This may be roughly repre- 

 sented by taking a piece of wide india-rubber tubing, and tucking 

 in one end of it. The space between the lower end of the gullet 

 and the base is called the stomach, and performs the function of 

 a digestive organ. But this is not all, for running across in a 

 radiating way from the body-wall to or towards the gullet are 

 a large number of fleshy partitions, which divide the space external 

 to gullet and stomach into a number of compartments. These 

 partitions, or mesenteries, are, however, perforated above, so as to 



