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 piles 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 feces, 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 infusorizv diatoms, and other inferior animalculee 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 
