SOME AQUATIC WORMS, ETC. 163 



CHAPTER VII. 



SOME AQUATIC WORMS, CH^ETONOTUS, AND CHIEONOMUS 

 LAKVA. 



THE collector of microscopical objects from the ponds 

 and slow streams is doubtless familiar with the appear- 

 ance of the bristle-bearing worms (Fig. 140), on account 

 of their general resemblance to those long-suffering 

 creatures which he in his youth impaled on a hook and 

 with them sought the nearest water. The extensive 

 bristles of the aquatic worms are an addition which 

 greatly lessen their resemblance to the common earth- 

 worm, and their transparency is another characteristic 

 that may temporarily mislead the observer, but their 

 elongated bodies and general worm-like aspect tell the 

 story. In addition to the bristles which most members 

 of this class possess, there are usually two or more 

 rows of long, curved spines (Fig. 141) on the ventral or 

 lower surface. These can be protruded or withdrawn 

 into the body at the possessor's will, and when pro- 

 truded are used to assist the worm to crawl. They are 

 therefore called the podal or foot spines. They may 

 not be noticed when retracted unless specially searched 

 for. Having observed them and the bristles in a row 

 on each side above them, the student need have no trou- 

 ble in knowing where to class the worms ; but with an- 

 8* 



