190 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
they have found appropriate places, they begin to change. One by one the bivalve 
characters become masked, and the little bivalves are transformed into the very 
long, worm-like shipworms which are found in wooden structures in salt water the 
world over. 
But along with the transformation the bivalve shell is preserved, though it is 
much modified as compared with other bivalve shells, and covers only a small part of 
the head end of the body. With it the shipworm excavates the burrow in the wood 
in which it lives, and seems equally able to penetrate the hardest or softest kind of 
wood with equal facility. As the wood is grated away by the shell, the small particles 
are taken into the digestive canal, and the debris is extruded through the anus; but 
whether it serves for food in any way is a question in dispute. During its life in the 
wood at least the larger portion of its nutrition is taken in through the tube which 
at rest hangs in the water, and consists of small animal, and especially vegetable, 
organisms. In thinking of shipworms, then, it should be remembered that the wood 
in which they form their burrows is primarily for their own protection, and that with- 
out this protection their long, naked, delicate bodies are defenseless. 
At Beaufort all kinds of unprotected wood become literally riddled in a very short 
time. Two kinds of worms are found there in great and about equal abundance — 
Teredo norvegica and Xylotrya fimbriata , whose mode of spawning has been already 
described. A very small proportion of specimens were of Teredo navalis , one of the 
common European forms, in which the eggs are retained in the gills of the mother 
during a considerable period of their development, perhaps almost till time for them 
to set into the wood. It is apparently this last species which the writer has found most 
abundant in Long Island Sound, though a considerable portion of Xylotrya fimbriata 
were also found. 
The breeding season in North Carolina, so far as determined, lasts at least till 
the middle of August and perhaps throughout the summer. That the latter is true 
is indicated by two sets of facts. In the first place, individuals were found with ripe 
sexual products during the early part of August, and the young derived from eggs 
laid at this time must continue to set till September or later. In the second place, the 
young were setting in the wood abundantly till the middle of August, a fact which 
indicates that the same continues to some degree for some time longer. Of course, 
from an economic standpoint, the period during which the wood is attacked is one of 
the most vital points to discover. 
The number of young produced is amaziug — estimated in one case, from a single 
very large female, at 100,000,000 — and while the greater part are lost before the 
setting stage is reached, yet the number that set is very great, and one of the most 
discouraging features in dealing with shipworms in a practical way. If the spat were 
of fairly appreciable size and set in but moderate numbers it might be feasible, by 
the careful removal of all old piles and other old timbers, to sufficiently reduce the 
number to a minimum. But when, under favorable conditions, over 100 to a square 
inch set where there is not room for more than one or two to reach maturity, it is 
easily seen what an excess is always present and how futile it is to try to combat the 
larvae before they enter the wood. The practical way, of course, is to prevent their 
entrance into the wood by protecting the wood with copper paint and sheeting. 
With small piles and timbers it would seem to be worth while to try various means of 
keeping the bark on the wood, which, so far as I know, has not been done; for it is 
well known that as long as the bark is on timbers they are not attacked by shipworms. 
