38 



d. The Mantle and Siphons, 



In the adult "Ship-v.'orm" (fig. 3) the mantle forms a 

 verj- lonr, and veiv delicate tube, which stretches from the 

 anterior edge of the shell, to tlie ends of the siphons, 

 which are modifications of the mantle, as in other forms 

 of Lamellibranchs. This tube is open only at the anterior 

 end, the pedal opening for the protrusion of the foot; and 

 at the ends of the siphons, the inhalent and exhalent 

 openings. It was formerly a much debated question, how 

 mxich of this tube should be considered body proper, and 

 hovr much siphons. In the lif^t of our present knowledge, 

 it is easy to see that the muscular collar marks off the 

 end of tlie body and the beginning of the siphons. 



The mantle of Teredo has undergone more differenti- 

 ation than in any other Lamellibranch. The anterior edf;e 

 is thickened, as in other forms, and secretes the teeth, 

 the edges of the valves andthe epidoiTiis. The very deli- 

 cate part iHiderlying the shell and stretching to the si- 

 phons, secretes the inner layers of the shell, and the 

 calcareous tube lining the burrow. Witliin the slioll cav- 

 ity, induplicatures secrete the apophyses and at the sane 

 time absorb part of them as they change shape and position: 



