17 



character, to take upon itself the sole purpose of burrow- 

 ing. In specimens 2 mm. lonr, , the shell is still a quart- 

 er of the length; in specimens four feet long, the shell 

 is an inch or less in length. With the loss of protection 

 by the shell, other means are acquired. In a general way, 

 the burrow offers the i)rotection afforded by the sliell in 

 other forms. But the very delicate tissues of the mantle 

 wovild be injured by the rough surface of the wood, and so 

 as the body elongates, it secretes around it a constantly 

 thickening calcareous tube, v/hich lines the v/hole burrow 

 except the anterior end, v/here the mantle is somewhat less 

 delicate; and where the tube fades out and the burrov/ is 

 being constantly enlarged. 



When the young "'.Vorm" enters the wood, it penetrates 

 vertically to the surface, but soon bends its course, so 

 that within two inches, usually, it becomes straight and 

 the worm bores with the grain. Individuals that enter the 

 wood on end, cut across tlie grain from the start, so tliat 

 their burrows are straight, unless they are turned from 

 their course by obstructions of any sort. If these are 

 met, the course is changed so that the burrows may become 

 very tortuous. When the "J'hip-v/orm" is in danger of bor- 



