WRIGHT—ON TUBIPORA MUSICA. DANE 
The polyp consists of eight pinnate tentacles, each tentacle with 
from fifteen to seventeen pinne on either side; these tentacles are 
thickly studded with spicules of an oval shape, flat, somewhat longer 
than broad; they closely resemble the lenticular spicules of Kélliker : 
they are met with all over the tentacle, down the centre of which 
there is one compact row, forming as it were a midrib; they are often 
slightly compressed in the centre, so as to form a figure of eight. In 
the centre of the tentacles is the mouth, with a slightly raised circular 
lip. When the polyp is alarmed, the tentacles are first closed together, 
and then the polyp sinks down quite into the tube; as it becomes 
more completely retracted, it draws in after it the uppermost portion of 
the tube itself, inverting this and folding it in, until the open mouth 
of the tube is thereby completely filled. It is, of course, only the yet 
spicular, and not the solid portion of the tube that is thus inverted ; 
and the folds thus formed equal in number the tentacles. Ihave more 
than once traced these spicular portions up to the very base of the 
tentacles, where the fusiform spicules end, and the characteristic 
tentacle and body spicules commence, these spicules thus forming a 
series of triangular spaces, the bases of which join on with the har- 
dened edge of the tube, and the apices are situated at the base of each 
tentacle. The spicules secreted by this portion of the ectodermic 
layer are of several sorts:—First, the warty fusiform spicule, so 
commonly met with in the Alcyonide; these spicules will be 
found in all stages of growth and of coalescence: thus at the upper 
portion of the edge of the tube, where it is non-retractile, the cal- 
careous tissue will be found to consist of a series of them, partially 
joined together, and making a kind of coarse open network (fig. 10),. 
which, on being macerated in caustic potash, does not fall to pieces ;. 
but the retractile portion, on being subjected to the same treatment, 
breaks up into a mass of minute individual spicules (fig. 8). The red 
colouring matter would appear not to reside in these latter spicules ;. 
for those that I have examined are colourless, presenting in this a 
marked contrast to the spicules of Melithea coccinea, which retain 
their red or yellowish-red colour after being exposed to the action 
of the caustic alkali. A second form of spicule is met with in the re- 
tractile portions of the tube; it closely resembles that form of spicule 
described by Kolliker as occurring in Eunicea fusca (Taf. 18. fig. 19), 
which I think might be called ‘‘shuttlecock.” While all the forms of 
spicules met with seem to occupy certain definite portions of the ecto- 
dermic layer, yet there is an evident gradation between them, from the 
smooth fusiform spicule to the most irregularly warty forms, which 
leads naturally to the inference that all these forms are but different 
stages of growth, by the aggregation of new calcareous material, until 
the solid tubular structure so long known to us is at last reached. 
The mouth, which is circular, is distinctly marked, and leads into 
the stomachal cavity, which is small; the stomachal cavity is sepa- 
rated by a thin and delicate membrane from the general body cavity. 
I have not been able to determine with exactness the number of 
