156 ERRANTIA. 



PART III. 



On the back of the worm there is a sort of shield, 

 the sides of which bear seven pairs of wart-like feet, 

 which are perforated for the working of protrusile mi- 

 croscopic bristles (fig. 134) . Their upper parts are double- 

 edged, with a groove between them, and serrated with 

 close-set teeth. The organs of retreat are much more 

 complicated and numerous. Mr. Gosse has computed 

 that there are about 1,900 blades on the seven pairs of 

 feet, each movable at the will of the worm, and that 

 there are nearly 10,000 teeth hooked into the lining of 

 the tube when it wishes to retreat. . The manner in 

 which it comes out of its tube and retires into it again 

 is the same as that employed by the earth-worm. 



There are twenty-four genera of the order Errantia, 

 or wandering sea-worms. Multitudes swarm on every 

 coast; they have considerable muscular strength, and 

 are highly irritable ; some are called sea-centipedes, from 

 the number of their feet and length of their segmented 

 bodies, which are slender, and vary from a few inches or 

 less to thirty-five or forty feet. They are generally 

 coiled up under stones, or wander by the slipperiness 

 of their smooth skins through masses of sea-weeds or 

 shells at low tide. In most of them the rings are de- 

 cidedly marked ; the first and last segments are unlike, 

 while the rest are mere repetitions one of another. 

 Their locomotive organs are a pair of perforated fleshy 

 warts on each of their numerous segments, through 

 which groups of rigid, simple or barbed bristles are pro- 

 truded and retracted. 



The Errant Worms have a distinct small head with 

 a mouth, or rather an orifice, on the upper side of it, 

 through which a cylindrical gullet is from time to time 

 turned inside out, forming a kind of pear-shaped bag, 

 whose surface is studded with secreting glands ; and its 

 extremity, which is perforated, is surrounded by a muscle 

 that contracts strongly on whatever it is applied to, and 



