323 



to which they may become attached they cHng to one another. In this way a ball of 

 a varying number of organisms is formed. There may be onl>' two or three, or a 

 dozen or more, indi\ithials together in such a balL It seems probable that this be- 

 havior is an expression of a reaction which leads the organisms to attach to all sorts of 

 substances. Those which happen to attach to wood are able to bore into it, and become 

 established there, and so survive. 



The distribution of Linuioria in driftwood offers better chances of success than 

 obtains in the distribution of detached organisms. Pieces of infected driftwood are 

 fretiuentK- found, carried by the wind .uid tidal currents, between the piles of a wharf. 

 Here they may become caught and subjected to severe erosion by the pounding of the 

 waves. The superficial layers of wood which are more friable are thus worn away, and 

 a large number of Limnoria liberated. It is here that the peculiar spiral and irregular 

 course of swimming affords added possibilities of the organisms' becf)ming attached 

 to a nearby pile or other structure. 



It may be assumed, then, that distribution from wharf to wharf, and from locality 

 to locality within a harljor, is accomplished in considerable measure through the agency 

 of infected driftwood. The swimming abilities of Limnoria, and tidal currents, may 

 account directly, however, for distribution cner shorter distances, as among the piles 

 of an infected wharf. A few piles of a wharf having become infected, they may serve 

 as a source for the gradual infection of the entire submerged structure. 



TlllC MK( ll.WlSM OF BORIXG 



The mechanical process b\' wliit'h Limnoria constructs its burrow has been ol)- 

 ser\ed in the case of individuals making an attack on a piece of Douglas fir. We were 

 able in one case to watch an animal under the binocular without flisturbing it for 

 several days. 



The body is firmly held in position by the peculiar arrangement of the legs and 

 claw-like feet. The claws of the first three pairs of legs are directed backwards, while 

 those of the four remaining legs are directed forwards. This arrangement permits 

 of a very firm and tenacious attachment to a piece of wood. The legs of the fourth pair 

 are directed more laterally than the others, giving support in this direction. Once 

 they have become attached to the surface of a piece of wood it is found to be very 

 difficult to wash the animals off with a stream of water, even though the force of the 

 current be much greater than that which would normally be produced by the wash of 

 the waves. The mechanism of attachment is of greatest service to the animal during 

 the early stages of excavating the burrow, when it is on the exposed surface of the 

 wood and entirely unprotected. 



In the boring process itself there is a very vigorous action of the moulh jKirts, 

 especially the mandibles and maxillipeds, combined with a slow turning motion of the 

 head. Details of the action of the mouth parts are difficult to observe, as a sufficiently 

 concentrated light to enable them to be seen disturbs the organism and it ceases its 

 activity. We have been able to see, however, that in boring the head is pushed forward 

 against the wood, the mandibles are brought into action, and then a quicker retractile 

 motion is given the head. The posterior part of the body is moved very little and the 

 turning motion of the head confines the boring to a limited area which becomes the 

 burrow. 



By carefully examining the edges of a burrow in process of construction one can 

 see small but very definite serrations made by the pointed tips of the paired mandibles. 

 Douglas fir shows these serrations particularly well, since the surface wood alter 

 soaking is generally reddish and contrasts well with the yellow wood exposed in the 



