126 THE BIOLOGY OF THE ANIMAL 



Do you find them in all segments ? In which di- 

 rection do they point? Do all point in this di- 

 rection ? How many setae in the girdle ? 



Remove a seta from an anterior segment, 

 mount it in a drop of water on a slide, and ex- 

 amine under a low power. What is the shape 

 of a single seta ? How do its ends differ ? Is 

 the seta attached to the cuticle? Examine un- 

 der a high power and study the structure. 

 Draw a seta magnified. 



g. The apertures. 



1. The mouth. — "What is its position? What is 



the direction of the opening ? Shape ? Ex- 

 amine the prostomium or proboscis. What 

 is its position ? Shape? How formed? Exam- 

 ine the peristommm with a lens. What is its 

 structure 1 



2. The anus. — Position? Shape? Compare with 



the mouth. 



3. The dorsal pores. — Strip the cuticle off the 



dorsal surface and look for these pores in the 

 median line in the grooves between the seg- 

 ments. They may frequently be detected by 

 gently squeezing the worm between the fin- 

 gers, which causes some of the fluid of the 

 body -cavity to ooze out of these openings. 

 How many pores does each segment have? 

 Are all of the segments provided with them ? 

 Where is the first pore ? The last ? 

 Indicate the pores on your outline drawing. 



4. The sexual apertures. 



{a) The opening of the vas deferens or duct of the 

 testis. — With a lens look for a pair of openings, 



