Annulata. 101 



modes of locomotion : (a) they creep along with a gliding movement 

 like a snail ; () they swim by a graceful undulatory motion ; (c) they 

 travel by a " looping " action, somewhat as in " measuring worms," 

 holding on alternately by the anterior and posterior suckers, some 

 leeches thus progressing actively. 



Other Annulate Worms. There are many annulate worms, mostly 

 marine. Some are free-swimming, while others live in tubes which 

 they form of mud, sand, or limestone. Many of them have beautiful, 

 feathery gills, sometimes distributed along the body, but in the tube- 

 inhabiting forms more frequently at the head end. Many sea worms 

 are phosphorescent, emitting a vivid green light. 



CHARACTERISTICS OF ANNULATA. 



1. The body is bilaterally symmetrical; there are also 

 distinct anterior and posterior ends, and dorsal and ventral 

 surfaces. 



2. The body is segmented (except Gephyrea). 



3. 'there is a distinct body cavity, divided by partitions 

 into as many compartments as there are segments. 



4. There is a well-developed blood-tube system for the 

 circulation of blood. 



5. A nervous system is present, consisting of cerebral 

 ganglions, esophageal collar, and ventral nerve cord. 



6. There are tubular kidneys in each segment. 



CLASSES OF ANNULATA. 



I. Oligochaeta (few bristles earth- 

 f Class i. Chsetopoda (bristle- J worm). 



footed). ( 2 . Polychasta (many bristles Nereis). 



Annulata. x Class 2. Gephyrea. 



I Class 3. Archi-annelida. 



V Class 4. Hirudinea the leeches. 



