NOTES ON A PRCULIAR FORM OF POLYZOA, 13 
In this particular species it will also be seen that the 
growth of the zoarium commences with an enormously elon- 
gated zocecium, from the bottom of which two prolongations 
are continued, which at the upper part are slightly calca- 
reous, but below become altogether chitinous or horny, and 
exactly like the other radical tubes. In fact, the branched 
termination shown in the figure belongs to one of these 
initial tubes as they may be termed. 
That the radical and connecting tubes, like the avicularia 
and vibracula, represent modified zooids, is, I believe, gene- 
rally admitted; nor can it be denied in this case that 
each successive joint or internode is a distinct zooid. In 
confirmation of this view I would take this opportunity of 
citing a very striking exemplification. This is afforded in a 
species of Carbasea (C.ovoidea, Bk.), in which, from the edge 
of the fronds, may frequently be seen numerous filamentous 
tubular processes, in all respects homologous with radical 
tubes, and like those destined to afford attachment to 
foreign bodies, or between the separate fronds themselves. 
A portion of the edge of a frond of this Carbasea is shown 
in fig. 9,in which it will be seen that cells of irregular 
form, and never containing a polypide or other structure, 
beyond the usual granular endosare and branching fibres, 
lie along the border. And that from some of these aborted 
cells (for they cannot be termed zocecia) tubular-jointed fila- 
ments arise, each of which may, in fact, be considered as repre- 
senting one of the longitudinal series of zocecia in the frond. 
At @ a short tubular process is seen from which two 
tubes arise, exactly in the same way that two zoccia arise 
in the course of the longitudinal series of ordinary zocecia ; 
and what is very remarkable, as proving the homology of 
these aborted zocecia with those of the ordinary kind, at @ 
the first internode of one of the filaments is actually fur- 
nished with a semicircular lip, although there is not the 
faintest indication of muscles or polypide in the interior. 
The growing end of the tubular filament presents a granular 
substance in the interior (0), precisely like that with which 
all the young budding zocecia are filled. 
These marginal cells and their tubular prolongations 
appear to me to afford the clearest possible evidence of the 
true nature of the radical tubes and clasping organs of the 
Polyzoa.! 
Note.—Since the above was written I have noticed in a 
1 In Bicelluria and in Notamia it may almost be said that the inhabited 
part of the zocecia is simply a dilatation at one part of the internode of 
a radical tube, which is continued to the ultimate extremity of the branch. 
