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," I 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 for- 

 tress, 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 dis- 

 tinct 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 



