14 GENERAL BIOLOGY. 



tamerism or serial symmetry). Count the 

 number of somites. 



2. Modifications of the somites : 



(a) At the extreme anterior end a smoothly- 

 rounded knob, the prostomium. 



(6) Swellings on the ventral side of some of 

 the somites between the 7th and the 

 19th, the capsulogenous glands. 



(c) Between the 28th and the 87th somites 

 a swollen region, the clitellum. 



3. The anterior and posterior ends are not 



alike (antero-posterior differ entiation). 



4. The dorsal and ventral sides are unlike 



(dorso-ventral differentiation). 



5. When the worm is placed with the ventral 



side down a longitudinal vertical plane 

 will divide it into similar right and left 

 halves (bilateral symmetry). 



6. The stiff bristle-like setae: felt by drawing 



the worm gently through the fingers. 

 With the naked eye or a hand-lens note the 

 arrangement of the setse. 



7. The openings to the outside : 



(a) The mouth: close to the anterior end on 



the ventral side below the prostomium. 



(b) The openings of the seminal receptacles: 



on each side between the 9th and 10th 

 and the 10th and llth somites (four 

 openings; difficult to make out). 



