94 BARNARD 



a greater resistance than softwood against crustacean attack, and while 

 the tiny flattened form of Limnoria may quickly burrow its way to a 

 safe depth, Chelura, under the same circumstances, would normally re- 

 main too long exposed to molestation from predatory enemies." Two 

 factors must be considered here: first, that chelurids are restricted not 

 only from hard woods but from smooth, soft woods as well ; and second, 

 that the shape of the animal probably has little to do with its boring 

 ability, which is determined by the activity and habits of the borer, by 

 the fact that it is a browsing type of borer rather than by its shape. 

 The rapidity with which Limnoria encloses itself in a burrow in a short 

 time as compared with the poorly developed excavations of Chelura 

 seems difficult to explain on any other basis than the habit of the lim- 

 noriid to provide its own protection. On the other hand, the wood- 

 digestability of limnoriids may be less efficient than that of chelurids 

 and more wood needs to be consumed by the former. The feces of 

 chelurids are darker than those of limnoriids but this may be explained 

 by the fact that chelurids browse on the surface wood which has be- 

 come darker through the action of the seawater. 



One further possibility must be considered : that chelurids might be 

 browsing on microscopic organisms which grow on the wood and the 

 ingestion of woody matter is a consequence of the scraping off of this 

 other food material. Continued exploration of the habits and physiology 

 of both limnoriids and chelurids is needed to answer these questions. 



SUMMARY 

 1. Although Chelura terebrans has not been found living in nature 

 in the absence of Limnoria, reproducing populations can be cultured 

 separately in the laboratory and maintained at least two years. 



2. The browsing, furrowing action on wood of C. terebrans con- 

 trasts strongly with the progressive tunneling of limnoriids. 



3. The inability of C. terebrans to excavate a protective burrow in 

 a short time prevents its successful infestation of marine timbers until 

 limnoriids have prepared holes large enough for invasion by adult che- 

 lurids. 



4. Adult chelurids invade marine timbers first, juvenile animals 

 not appearing until some time later and apparently only as offspring of 

 adults already present. 



5. The surface appearance of eroded timber cannot be relied on in 

 all cases to indicate the presence or absence of chelurids. 



