88 GENERAL BIOLOGY 



these distinctions equally marked in all parts of the body? 

 Are the two sides of the animal alike? If so, it is said to 

 be bilaterally symmetrical. 



3. Setae are short, horny spines embedded in the body 

 wall but projecting a little. They aid in locomotion. They 

 may be felt by rubbing the finger over the ventral surface 

 of the body. If this region is examined with a lens the 

 seta? will be seen as tiny brown spots. How many are there 

 on each somite ? How are they arranged ? 



4. Openings of the Body. The mouth will be found on 

 the ventral side of the body at the first somite. What is 

 the position of the mouth relative to the prostomium? At 

 the end of the last segment of the body is the anus, the 

 posterior end of the digestive tube. On the ventral side 

 of the fifteenth somite are the openings of the testes, called 

 the sperm ducts, one on either side surrounded by swollen 

 lips. The ovaries open through the oviducts on the ventral 

 side of the fourteenth somite, but they are not surrounded 

 by swollen lips. The openings to the sperm receptacles, 

 of which there are two pairs, are situated in the grooves 

 between the ninth and tenth and the tenth and eleventh 

 somites, and are on the sides of the animal in the same line 

 as the lateral rows of setae. 



The openings of the excretory organs are found in each 

 segment on the ventral surface a little anterior to the outer 

 seta of the ventral row. They are not very plain, but with 

 a lens will usually show well on some somites. The dorsal 

 pores, which communicate with the ccelomie cavity, are in 

 the middorsal line and open in the grooves between the 

 somites. 



Draw the anterior and the posterior parts of the body 

 to show all that you have observed. 



