ANNULATA. 219 



the performance of function in the group. What evidences 

 of muscular action are manifest? How is locomotion effected? 

 Position and mode of action of setae? Study the capture of 

 food; how is its progress through the digestive tract, and its 

 elimination therefrom effected? Do you discover any circu- 

 lation of the blood ? Direction of flow? Evidences? How ac- 

 complished? Test for ability to receive and respond to stimuli 

 of different sorts. Where are new segments formed? Dis- 

 cover, if possible, instances of fission, by which new individuals 

 are formed. 



254. The Leech. The leech may be studied and compared with the 

 earthworm as to its external features, its habits, mode of locomotion, and 

 the like. If large specimens can be had some members of the class might 

 substitute it for the earthworm and the results of the studies brought into 

 comparison. 



255. Nereis. If specimens of Nereis can be obtained this worm should 

 be compared with the earthworm. (Even two or three good specimens 

 may be made useful from year to year as demonstration both of external 

 and internal structure.) 



Note especially: 



(a) The specialization of the anterior end; proboscis, mouth, jaws, 

 palps, cirri, eyes, antennae. 



(&) The fleshy supports of the bristles, parapodia. 



DESCRIPTIVE TEXT. 



256. The Annulata are separated from the unsegmented 

 worms by the possession of a series of segments or metameres 

 which show on the exterior as rings, and contain similar or 

 homologous organs or similar portions of a continuous organ. 

 There is also a more uniform development of the ccelom than 

 in the lower worms. They differ from the ccelenterata and 

 echinoderms in having bilateral rather than radial symmetry in 

 the adult condition. The development is often direct, but in 

 many, especially the marine forms, there is a metamorphosis. 

 The larva has a peculiar balloon-shaped form, known as the 

 trochosphere (Fig. 104, E), similar in some respects to the 

 Rotifers. 



257. General Characters. 



i. Body elongated, bilaterally symmetrical and segmented. 



