THE SERTULARIAN ZOOPHYTES OF OUR SHORES. 
225 
miniature forest surrounds the original stock, united with it in 
one. compound organism and sharing a common life. In some 
of the large foreign species, the tree-like shoots attain a height 
of two or three feet, and bear some millions of polypites, all 
evolved by continuous gemmation, and the offspring of a single 
germ. These facts in the history of the zoophyte have their 
pararlk^l in that of the plant. The multitude of polypites 
united in one organism answers to the myriads of leaves upon 
the tree, and in both cases the manifoldness is due to successive 
buddings. Other correspondences will appear as we proceed. 
All the zoophytes belonging to the tribe now under considera- 
tion are composite beings in their adult state. They form com- 
munities of greater or less extent, the organisation and economy 
of which we shall endeavour to explain. The horny tree-like 
tufts which we gather on the shore are the external skeletons, 
as it were, of the zoophyte. They consist of ramified tubular 
cases, which inclose and protect the soft portions of the animal. 
Examined with care, the stems and branches are found to bear 
at intervals small cup-like receptacles, which give them a serru- 
lated appearance (Plate XLVI. fig. la). These are known as the 
calycleSf and serve as the homes of the multitude of minute 
Hydrce, that combine in these composite organisms to form a 
kind of federal republic (Plate XLV. fig. I 0 ). Through the 
entire extent of the tubular investment, a thread of animal sub- 
stance passes in the living state, pervading every minute branchlet, 
and linking together as one organic whole the tenants of the 
many calycles scattered over the structure. This common flesh 
(coenosarc) (Plate XLV. fig. lx), permeating the principal 
stem and ramifying through every portion of the arborescent 
shoots, is the essential part of the zoophyte. The horny cuticle 
(Plate XLV. fig. ly) is an excretion from its surface; the hydrae 
bud from it, and when destroyed are renewed from its prolific 
pulp ; and penetrating its substance throughout runs the cavity 
in which the nutrient juices circulate. This central canal extends 
to the base of the calycles, and there communicates with the 
stomachs of the hydrae, from which the food captured and 
digested by them passes into it, and is distributed through the 
organism (Plate XLV. fig. 2a). The alimentary zooids, to 
which is assigned the office of purveyors to the commonwealth 
— that procure and prepare the pabulum on which the healthy 
development of the colony depends — are structurally identical 
with the Hydra of our fresh waters, and are known in the 
terminology of the Hydroida as the polypites (Plate XLV. 
figs. 2, 3). They are lodged in the calycles,* which we have 
The presence of a calycle or protective theca for the pol}-pites is cha- 
racteristic of that section of the zoophytes to which this paper is devoted 
