66 INVERTEBRATE ANIMALS. 
out the power of voluntarily changing its place, whilst the re- 
productive process is considerably different. In the majority of 
the Corynida, however, the hydrosoma is compound, consisting 
of a greater or less number of separate polypites or zodids, all 
connected with one another by a common flesh or coenosarc, 
and all forming parts of a plant-like rooted colony. In some of 
the Corynida the polypites are naked, but in most cases the 
coenosare is protected by a horny-looking chitinous* envelope 
or “polypary,”’ as in 7ubularia indivisa (fig. 17). In no case, 
however, is this horny covering so 
SUZ prolonged as to form little cups in 
we \W which each polypite is contained. 
ZN Os It always stops short at the bases of 
the polypites, and in this way the 
s Corynida can always be distinguish- 
ed from their near allies, the sea-firs 
(Sertularida). 
As a good example of the Cory- 
nida, the common pipe - coralline 
(Tubularia indivisa) may be taken. 
In this animal (fig. 17) we have a 
gregarious zoophyte consisting of 
‘numerous clustered horny tubes, 
fixed by their bases to shells or 
stones, and inhabiting most of our 
British seas. The tubes are usually 
unbranched, though often consid- 
erably interwoven together. Each 
tube is filled with a soft semi-fluid, 
reddish coenosarc, and gives exit at 
its distal extremity to a single poly- 
Fig. 17.—Fragment of Txbularia pite. The polypites are bright red in 
endivisa, natural size. colour, and are not retractile within 
their tubes, the horny polypary extending only to their bases. 
The polypites are somewhat conical in shape, the mouth being 
placed at the apex of the cone, and they are furnished with two 
sets of tentacles. One set consists of numerous short tentacles 
placed directly round the mouth, the other is composed of 
from thirty to forty tentacula of much greater length arising 
* Chitine is a substance which is nearly allied to horn, but is distinguished from it 
by the fact that it is not soluble in caustic potash. 
