Natural History of British Zoophytes. 231 
commonly by filiform tentacula : alimentary canal variable, where 
there is an intestine the anus opens near the mouth : assexual ; gem- 
miparous: aquatic. The individuals (Polypes) of a few families 
are separate and perfect in themselves, but the greater number of zoo- 
phytes are compound beings, viz. each zoophyte consists of an indeji- 
nite number of individuals or polypes organically connected and placed 
in a calcareous, horny or membranous case or cells, forming, by their 
aggregation, corals or plant-like Polypidoms. 
In this definition there are two parts which require our particu- 
lar attention the Polype whose presence is essential, and the Po- 
ly pidom* which is the house or support of the polype, and which, 
though commonly present, is yet not necessary to the existence of 
a zoophyte. To the structure and functions of the former we limit 
ourselves in this chapter ; and should the reader find the outline 
given in relation to some of the families too slight and sketchy, we 
may advertise him that he will find it filled up with greater detail 
in the observations which it is intended to prefix to each separate 
order. 
The description usually given of the structure and functions of 
polypes in general has been derived principally from an examina- 
tion of the Hydra a naked species which inhabits ponds and ditch- 
es. A polype is thus represented as being a somewhat globular or 
cylindrical body of small size, of a homogeneous gelatinous consist- 
ence, and very contractile, in the centre of which there is excavat- 
ed a cavity for the reception and digestion of its food. The aper- 
ture to this cavity is placed on the upper disk of the body, and is 
encircled by one or two series of filaments or tentacula which are used 
to capture the. necessary prey, and bring it within reach of the lips ; 
while the opposite end serves the purpose of a sucker to fix the 
creature to its site, or being prolonged like a thread down the hol- 
low sheath, to connect it with its fellow-polypes of the same poly- 
pidom, which by this means become compound animals, " the whole 
of whose parts are animated by one common principle -of life and 
growth." There are no organs of sense, no limbs appropriate to lo- 
comotion, no circulating vessels, no nerves, nor lungs, nor gills, no 
chylopoetick viscera, nor intestine, for there is " but one conduit 
both for purgation of their excrements, and reception of their sus- 
tenance ;" and when to these negations there is to be added the 
want of generative organs, a being of simpler organization than the 
* I borrow this term from the translator of Lamouroux's work on Coral- 
lines. The Rev. Mr Kirby uses the word Polypary to express the same thing. 
Both of them are translations of the Poly pier of the French naturalists. 
