BORING LIFE 143 



deep, and are not lined with shell. Although the burrows 

 are apparently made in the same manner as Teredo, by- 

 means of the shell, there are no pallets and the animals 

 cannot digest the wood. The same is true of the third 

 type of Molluscan borer, Martesia. This is a native of 

 the tropics and is very like a small mussel in appearance ; 

 its burrows are not generally more than two and a half 

 inches long and one inch wide, i.e., the size of the animal 

 which lives within them. Neither of these animals has 

 attained the efficiency of Teredo as a borer and both seem 

 to seek the wood mainly as a means of protection, and 

 not also as a source of food as does the Ship worm. 



There are a number of Crustaceans which habitually 

 bore into wood. One of these stands out pre-eminent, like 

 the Shipworm amongst the Molluscan borers, on account 

 of its ubiquity and the great damage that it does. It is 

 the Gribble, Limnoria lignorum, a little creature resembling 

 a miniature woodlouse, usually between one eighth and one 

 sixth of an inch long and with a semi-cylindrical body 

 divided into segments (Plate 52). It has seven pairs of 

 short legs each ending with a sharp, curved claw by means 

 of which the animal holds on to the sides of the burrow. 

 Beneath the hinder end of the body there are five pairs 

 of legs each carrying two broad plates which act as gills, 

 these keep up a continuous movement during the life of 

 the animal and so constantly renew the water needed for 

 respiration. The animal bores into the wood by means of 

 a pair of stout " mandibles, " one on either side of the mouth. 

 These are not identical, for the one on the right has a sharp 

 point and a roughened edge which fits into a groove with 

 a rasp-like surface in the left mandible, the whole providing 

 a " rasp-and-file " combination, as shown in Figure 31. 



Unlike the burrows of the Shipworm, those of the Gribble 

 are always the same width throughout, so that it appears 



