SOME AQUATIC WORMS, ETC. 197 



and constantly waving to and fro beyond the edge of 

 the little tubular chimneys which they erect. These 

 little towers are often conspicuous objects on the sur- 

 face of the mud in shallow still water, the worms in- 

 stantly disappearing into them at the slightest disturb- 

 ance. Among certain French and German writers on 

 the subject, there is a difference of opinion as to which 

 end of the worm is buried and which end protrudes into 

 the water. As the protruding parts are continually 

 moving, and as the worms also dart into the mud with 

 such astonishing swiftness, to decide the matter is rather 

 difficult. 



The bristles are comparatively short, and appear to 

 be arranged in a single row on each side of the body, 

 whereas there is really an additional row of podal spines 

 on both sides of the worm. These podal spines are en- 

 tirely retractile, and are therefore often overlooked un- 

 less specially searched for. Even then it will perhaps 

 be necessary to compress the worm rather forcibly be- 

 tween the slide and the cover-glass before they will be- 

 come conspicuous. They are forked, and but slightly 

 curved. 



With very high magnifying power (about eight hun- 

 dred diameters) some of the bristles present a curious 

 aspect. The free extremity is widened and forked, the 

 two prongs of the fork being apparently connected by a 

 thin membrane which is longitudinally striated. Some- 

 times this membrane splits into fine hairs. These wid- 

 ened bristles are most common on the young worms. 



