34 PRACTICAL ZOOLOGY. 



straighten (extend) the abdomen. Pick it away care- 

 fully with the forceps. 



7. Running lengthwise, in the middle line, is the 

 intestine, a thin-walled tube, often of a dark color 

 from its contents. Trace it back to the anus, and 

 forward to the stomach. Carefully remove the in- 

 testine. 



8. A large mass of muscle remains. This is composed 

 of the muscles that bend (flex) the abdomen. Draw 

 the point of a knife-blade or dissecting needle along 

 the middle line of this muscle, along the bottom of 

 the groove in which the intestine lay. After a thin 

 layer has been cut through, the whole muscle may be 

 easily separated into two rolls the whole length of 

 the abdomen. Pushing these carefully aside, find in 

 the middle line of the floor of the abdomen a slender 

 white nerve cord, with enlargements at intervals. 

 How many of these enlargements, ganglia, are there 

 in the abdomen ? What relation do the ganglia have 

 to the . segments ? Observe the branches, nerves, 

 given off to the muscles on each side. Trace the 

 nerve cord forward to the thorax, where it disap- 

 pears in the hard framework of the floor of the 

 thorax. Break away as much of this framework as 

 is necessary to follow the cord to the head. Make 

 out that the cord is double. How many ganglia are 

 there in the thorax ? Note the branches extend- 

 ing to the legs and other organs. From the large 

 ganglion back of the gullet trace two branches for- 

 ward, one on each side of the gullet, till they unite 

 in a large ganglion above the gullet, thus forming 

 the esophageal collar. From the ganglion above 



