4 o8 THE POPULAR SCIENCE MONTHLY. 



as Deshayes has pretended, an animal having very few if any muscles, 

 is, on the contrary, richly provided with those organs. There are the 

 longitudinal and transverse muscles through the whole length of the 

 mantle, a true sphincter (Fig. 10, c) at the base of the siphons, a mus- 

 cular organ which receives and covers a part of the valves, two adduc- 

 tor muscles for the movement of bringing the valves together, and a 

 foot provided with a suction-disk and susceptible of extension and re- 

 traction truly a profusion of motive organs which one would not expect 

 to find in an animal which passes its entire life in a narrow canal which 

 it can never quit. Moreover, all these motive powers have only one 

 essential end, namely, to endow the teredo with the power of boring 

 his gallery his home. 



But all the muscles which we have enumerated do not cooperate to 

 that end in an equally direct manner. When water has entered by the 

 incurrent siphon, the animal can, by contracting the transverse mus- 

 cles of the mantle, force the water through the whole length of its body 

 up to the end of the gallery, and then drive it out by the excurrent 

 siphon. The teredo undoubtedly makes use of this as a means of get- 

 ting rid of the fine filings of wood which the valves of the shell have 

 detached. He can then draw back a little the anterior part of his body 

 by the action of the longitudinal muscular fibres, supporting himself by 

 the two palettes pressed against the inner walls of the calcareous tube 

 at a distance of two or three millimetres from the exterior opening, by 

 which the siphons project outside the wood. It is probable that the 

 teredo takes that position during his periods of repose, which come 

 from time to time, and which he uses for repairing his tools. 



The teredo possesses, on the other hand, the means of preventing or 

 hindering the outflow of water at will, so that its body, distended by 

 the liquid, occupies at that time the whole extent of the gallery, and his 

 anterior portion touches with the valves of its shell the end of the gal- 

 lery. In this position he can carry on his work of miner. He com- 

 mences then by extending his foot (Fig. 1, c?), which he fixes by suc- 

 tion against the side of the cavity. At the same time the valves sep- 

 arate a little ; then, while the foot draws the shell to itself and thus 

 presses its exterior surface against the wood, the valves close up again, 

 and the denticles with which they are furnished cut into the wood. 



In this labor there are still two peculiarities worthy of notice : First, 

 the limited extent of movement with which the valves are endowed, 

 their anterior extremities moving only a very short distance from each 

 other. But this circumstance, in view of the narrow space in which the 

 teredo works, gives him this advantage, that, by the rapid succession of 

 movements of opening and closing the shell, he attains his end namely, 

 to reduce the wood to an impalpable powder better than if each blow 

 of the instrument had a wider range. In the second place, we should 

 recall the fact that the directions of movement of the two adductor mus- 

 cles are at right angles, as are also the directions of the cutting surfaces 



