362 TEREDO NAVALIS IN NOVA SCOTIA — MURPHY. 



a direction perpendicular to the surface (Figs. 12 and 15-C) ; 

 then they generally turn about in order to follow the direction 

 of the woody fibres, usually upward, but sometimes downward 

 Although they do not enter into the earth or mud, one generally 

 finds the first traces immediately above the line of the mud in 

 which pile? are driven ; it is at this point that piles destroyed 

 by the teredo generally break off. 



" When the teredos are lodged in a piece of wood, one recog- 

 nizes them by very small holes on the surface, and the extremely 

 delicate tubes which project from them (Fig. 12, e, d). These 

 are the siphons, only one of which shows at first, the other ap- 

 pearing later. These siphons are generally kept outside the wood 

 in the water, but the slightest touch causes the animal to retract 

 them. One of them is shorter and larger than the other, but 

 they both seem to serve for the expulsion of the faeces, which 

 largely consist of particles of wood reduced to a very fine powder. 

 It is known that the teredo does not perforate wood for nourish- 

 ment, but only to procure a suitable abode ; the woody substance 

 detached in the boring, passes through the intestinal canal, and 

 then is expelled in the form of a very fine white substance by 

 one of the siphons, generally, according to M. Vrolik, by the 

 shorter, but sometimes by the longer. The long siphon appears 

 to serve principally for the introduction of food, which consists 

 of infusorise diatoms, and other inferior animalcule© which the 

 sea-water brings with it into the siphons. It is nevertheless 

 still uncertain whether the matter expelled through the longer 

 siphon comes directly from the intestinal tube, or is at first 

 introduced from outside with inflowing water to be expelled 

 again after a short sojourn inside. 



" The Teredo requires for respiration a clear, pure water. It 

 has often been remarked that piles placed in dirty, muddy water, 

 near drains, for example, are protected thereby. The water 

 should have, moreover, a certain degree of saltness; the teredo 

 cannot live in brackish water : that is a point to which we shall 

 return later. 



" The Teredo continues to grow in the wood ; while the gal- 

 lery which it forms presents near the surface a diameter of only 



