325 



the claw-like feet for attachment is particularly serviceable at this time. It is to be 

 noted also that those organisms which bore more rapidly arc more likely to survive 

 this comparatively critical period of their life. 



There is apparently a limit to the distance Linuwriu will penetrate into the 

 wood. The deepest burrows are generalK' within one-half inch of the surface. Burrows 

 extending three-quarters of an inch from the surface are not often found. This limita- 

 tion arises most probably from the difticultN' of obtaining a sufficient supply of water 

 with normal oxygen content in deeper burrows. Not only is the circulation of the 

 water hindered by the tortuous path it follows in coming into the deeper lying bur- 

 rows, but it is also partially deoxygenated by those organisms living in the more 

 superficial burrows. In this connection, one finds on observing the lateral walls of the 

 deeper burrows that numerous small holes have been made through them, connecting 

 adjacent burrows. These holes are not sufficient in size to allow the body of the 

 organism to pass through. They serve as an entrance for the currents of water pro- 

 duced by the action of the pleopods. The currents may be followed by placing some 

 silt or small pieces of debris near these entrance points. The currents draw the material 

 in around the sides of the animal, oxer tlie pleopods, and out through the entrance 

 to the burrow. 



As a result of these communicating passages the water circulates more freely and 

 the organism can burrow more deeply into the wood. As the superficial exposed layers 

 of wood are washed away more rapidly than the wood around the deep burrows, not 

 only are those burrows which were formerly the deepest given an increased supply 

 of sea water, but the majority of their inhabitants are left in place to continue the 

 attack. Those more exteriorh- situated are more likely to be washed away along with 

 the wood they are inhabiting. 



Since those organisms which bore more rapidU' become located in the deeper 

 burrows, differences in rate of boring may accordingly be operati\e as a sur\i\al 

 factor here, as well as in the initial stages of making the burrow. 



nic.KSTiox OF Wood 



As remarked abo\e, all of the wood particles rcnioxed b\- Limnoria pass through 

 its digestive tract. This raises the question of the probable utilization and digestion 

 of this wood for the maintenance of the organism. 



Wood appears to be the onh- substance which has e\er been lound in the digestive 

 tract of this organism. In the examination of a consideralile number of animals we 

 have not been able to detect any other substance, and so far as we know, no other 

 author has recorded finding anything except wood in the digestive tract of Limnoria. 



It has been shown by several authors that the digestive tract of Teredo contains 

 numerous diatoms and other plankton. On account of the very low protein content of 

 wood, it has been suggested that Teredo obtains protein material by the digestion of 

 these organisms. 



Limnoria possesses no mechanism for filtering out plankton from sea water, 

 such as that of the lamellibranchs. It must rely entirely, so far as we know, on what 

 is taken into the mouth by the action of the mandibles and associated mouth parts. 

 If Limnoria obtains its entire protein material from wood, it would be necessary for 

 it to ingest a very large amount of that substance. As pointed out above in discussing 

 the boring habit, much wood actuallv is ingested, and its passage through the digestive 

 tract is rapid. Such rapid handling of the wood appears to be the only means by which 

 sufficient protein can be f)btained. 



The carbohydrate requirements are probably supplied from the cellulose, ligno- 



