72 ZOOLOGY DIKECTIONS 



takes place outside the body of the worm, within the cocoon. The 

 cocoons are worked off the anterior extremity of the worms and 

 are deposited in moist places. Here the eg'gs undergo develop- 

 ment and give rise to minute immature worms which finally 

 leave the cocoons and burrow in the soil. 



CIRCULATORY SYSTEM 



1. The dorsal vessel may be seen as a small dark tube which 

 runs along the dorsal surface of the digestive tube. How far 

 forward does it extend ? 



2. Large lateral branches, '^ hearts," pass around esopha- 

 gus. At demonstration table examine a piece cut through the 

 body in the region of the hearts to see connection with ventral 

 vessel. 



3. In your own dissection find at least four pairs of hearts. 

 Draw a pair in optical vertical section to show their shape and 

 communication with longitudinal vessels. 



4. Parietal vessels may be found in the body wall and in 

 the wall of the intestine. 



5. Make a diagram of the main trunks of the circulatory 

 system. Nnmher the hody segments shown. 



DIGESTIVE SYSTEM 



1. The alimentary tract, a straight tube extending through 

 the body, has the following parts arranged in order from anter- 

 ior to posterior extremities: 



(a) Buccal cavity or mouth cavity, a thin-walled sac- 

 shaped structure communicating with the outside through the 

 mouth. 



(b) Pharynx, thick-walled region with muscles running to 

 the body wall. 



(c) Esophagus, slender and extending through a number 

 of somites, mostly hidden by the sperm sacs which may now be 

 removed by picking away the pieces carefully with a pair of fine 



