14 



idly. The foot becomes a pestle-shapod orr;:an which assists 

 the sliell in buiTowing. The sliell valves lose their power 

 of opening at tlio ventral side, 'anu by tivj (iovelopment of 

 knobs on the ventral and dorsal portions of either valve, 

 they are able to swing on each other at ri,p;ht angles to 

 the former direction. Meanwhile the shell gapes at both 

 anterior and posterior ends, for the protrusion of the 

 foot in front, and the siphons, and later the body, be- 

 hind. And on the anterior edges have been formed the small 

 teeth which at this and later stages are the mechanical 

 agents by which their possessor bores into the wood. This 

 transformation has taken place v/ithin two days fi"om the 

 time the larva has settled, and afterwards the animal rap- 

 idly becomes a "S!iip-wonn" , enlarging its buri'ow in the 

 v;ood as it increases in size. 



Rate of Growth within the V/ood.- The "r-hip-worm" in its 

 larval stages develops but slov/ly, but once in the wood, 

 it grows with remarkable rapidity. During its free life, 

 most of its energies seem devoted to active locomotion and 

 development; after attachment, it leads a sedentary life 

 and its c^o'irth is correspondingly rapid. The newly-attach- 



