Dr. A. Philippi’s Zoological Notices. 91 
branchia, which however has fixed itself in the neighbour- 
hood of the back, and has above the seam another narrow ap- 
pendix, which might be compared with the second branchia, 
and which half surrounds with its free margin the anterior 
closing muscle. The branchiz of both sides cohere in the 
seam with the posterior half. They are strongly and distinctly 
striped. Remarkably small is the mass of intestines which 
project free between the branchiez. See fig. 6, where this is 
separately represented. 
Respecting the formation of the spinoid tubes Sig. Scacchi 
says, in his memoir read to the Academy, which he has com- 
municated to me in manuscript, as follows :— 
** Rang is of opinion that the spinoid tubes served the pur- 
pose of allowing the exsertion of a kind of byssus, with which 
the animal fastened itself to the basis of its dwelling; but no 
observation supports this view, and I believe I may say with 
certainty that the Clavagelle have no byssus ; moreover, every 
one will easily conceive how useless this would be to them, 
since they cohere immoveably to one of their shells. Since 
they live in the midst of sea-acorns (Balani), which form a 
group of empty shells which grow one upon the other, it must 
necessarily happen that the Clavagella on increasing meets 
with the cavities of the surrounding Balani, when it absorbs 
or destroys everything round about in order to render its 
dwelling more spacious. Now observation has shown me, 
that when such cavities open near the animal, some fleshy 
fibres proceed from the great muscle which joins the margins 
of the mantle, and there direct themselves to the place where 
the cavity of the balanite is open, and form small calcareous 
tubes. ‘They generally terminate with two small branches 
which finally close, yet I have sometimes found in some a 
small aperture at the end. These tubes prevent the entrance 
of any foreign body, and distribute themselves like the roots 
of plants, so that those which come near to the inner surface 
of the Balani adhere to it; the others either remain free or 
attach themselves to sand, and any other foreign substances 
they accidentally meet with. It appears that but few days 
are necessary for the formation of these tubes, as among so 
many individuals which I have had occasion to examine alive, 
I have only twice had the pleasure to surprise the animal with 
the above-mentioned fleshy filaments, which lie in the tubes 
that were just formed ; and some other times I have met with 
some of these filaments, which having performed their office, 
were dried and now hung as appendices of the epidermis to 
the great muscle of the mantle.” These spinoid tubes serve 
then the animal to fix itself, and are consequently most 
