WORMS. 313 



conical stopper with wliicli it closes up its bottle as with 

 cork, when safe at home, and the lovely crown of gor- 

 geously coloured fans which it expands when it takes 

 (" the «/r," I was about to sav, but rather) the water. 

 i'ou are familiar, too, with the lightning-like rapidity 

 with which, while in health and vigour, the Serpula, 

 on the slightest alarm, retreats into his fortress, taking 

 care to clap the door to 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 pro- 

 trusion, and the sudden and swift retreat — so there 

 are two distinct sets of organs by which they are per- 

 formed. Shall I sacrifice one from this fine group to 

 demonstrate the mechanism ? Well, then, I carefully 

 break the shelly tube, and extract the AVorm unin- 

 jured. 



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, havino- 

 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 ex- 

 amined. 



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 

 U 



