105 
cells being very small, and situated on the room xl 
inner side of the hair-like joints placed in 
whorls round the fistulous jointed stem. 
The genera Cymodocea appear to be only 
Sertularice which have lost their cells. 
The last group of these kinds of Corals are 
the Fluviatile Polypiaria , characterized by their 
tentacula being numerous, long, simple, and 
retractile, and expanded in the form of a 
horse-shoe. They are inclosed in a long, 
tubular, horny sheath. This division includes 
two well-known Corals, both found commonly 
in England; Alcyonella , in which the coral 
forms a globular mass, composed of nume¬ 
rous hexagonal tubes placed side by side, and 
Plumatella , in which the tubes are solitary, or 
united in a creeping group. It is probable that 
the Plumatella may be only the young of the 
former, and M. Raspail has attempted to prove 
that Cristellaria and Difflugia may be also the 
same animal in its very young state. 
The common fresh water Polypes {Hydra) 
are distinguished from the other Polyparia by 
the body being naked, with only a very simple 
stomach, without any trace of any other organ¬ 
ization ; by the tentacula being long, simple, 
and very contractile; and by the animal repro¬ 
ducing its kind by buds springing from its ex¬ 
ternal surface. These Polypes appear to be the 
most simple animals in the creation, since the 
Infusoria 
