Dr. A. Philippi's Zoological Notices. 91 



brancJiia, 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 branchiae 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 branchiae. 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 Clavagellce 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 



