272 EVENINGS AT THE MICROSCOPE. 



closes up its bottle as with a cork, when safe at home, 

 and the lovely crown of gorgeously coloured fans which it 

 expands when it takes ("the air" T was about to say, but 

 rather) the water. You are familiar, too, with the light- 

 ning-like rapidity with which, while in health and vigour, 

 the Serpula, on the slightest alarm, retreats into his 

 fortress, taking care to clap-to the door after him. But 

 perhaps you have never had an opportunity of examining 

 the mechanism by which this rapid flight is effected. 



As there are two distinct movements performed by the 

 Worm, — the slow and cautious and gradual protrusion, 

 and the sudden and swift retreat, — so there are two 

 distinct sets of organs by which they are performed. 

 Shall I sacrifice one from this fine group to demonstrate 

 the mechanism % Well, then, I carefully break the shelly 

 tube, and extract the worm uninjured. 



Its form is, you perceive, much shorter and more 

 dumpy than you would have supposed from looking at 

 the tube ; and it is somewhat flattened, having a back- 

 and a belly-side. On the former there is a sort of shield, 

 the sides of which bear wart-like feet, — about seven 

 pairs in all, — which are perforated for the working of 

 protrusile pencils of bristles, similar in structure and in 

 function to those which we lately examined. 



Here is one of the pencils extracted. To the naked 

 eye it is a yellowish body with a satiny lustre ; and this 

 effect depends upon the light being reflected from a 

 number of nearly parallel lines, — the staves of the spear- 

 like bristles,- — which the eye cannot resolve in detail. 

 A drop of the caustic solution of potash cleanses the 

 bundle from the fleshy matter which would otherwise 

 obscure the vision, and now I place it on the stage. 



With this power of 400 diameters you see a multitude 

 — some twenty or thirty, or more — of very long, slender, 

 straight rods, of a clear yellowish horny substance, set 

 side by side, like a sheaf of spears in an armoury. Each 



