PUNT-POLES. 



45 



This worm lives in a shelly tube, which is lined with a 

 delicate membrane, up and down which it passes with ease, 

 ascending slowly, but generally descending with such wonder- 

 ful rapidity that the eye cannot follow its movements. The 

 latter movement will be explained in a subsequent part of the 

 book, and we will at present only treat of the former. 



If the v creature be removed from the tube, and carefully 

 examined, a number of projections will be seen, in each of 

 which is a perforation. If the animal be pressed, a slight 

 glass-like bristle passes through the perforation, and can easily 



PUSHING SPIKES OF SERPULA. 



BOAT-HOOKS AND PCXT-POLES. 



be removed. If properly treated, and placed under a high 

 power of the microscope, the tiny bristle resolves itself into 

 the remarkable object which is shown on the left hand of the 

 illustration. 



It consists of a number of spear-like rods, each having a 

 straight shaft, and a curved and pointed tip, deeply barbed on 

 the inner portion of the curve. These curious bundles of 

 spicules can be protruded or retracted at pleasure, and, as they 

 are all directed backwards, it is evident that when they are 

 pushed against the sides of the tube, either the points or the 

 barbs must catch against the membrane which lines the tube, 

 and so propel the animal upwards. When it wishes to 

 descend, it uses another set of implements, and withdraws the 

 first within their sheaths. 



This is exactly analogous to the mode of progression em- 

 ployed by punters, who, after they have placed the pole against 

 the bed of the stream, and run along the punt so as to push it 

 as fast as possible, immediately withdraw the pole, and take it 

 to the head of the punt, ready for another push. This, as the 

 reader will see, is exactly the plan pursued by the Serpula in 

 lengthening itself when it wishes to advance, and so to press 



