128 WORMS 



(3) Trace the digestive tract from the mouth to the 

 anus. That part extending from the mouth to about the 

 tenth segment is the pharynx. From this point to the seven- 

 teenth segment is the narrowest part, and is called the 

 esophagus, or gullet. This opens backward into a dilated 

 portion, the crop. Just behind the crop is another dilated 

 part, the gizzard. The remainder of the alimentary tract 

 to the anus is the intestine. 



(4) Notice a brownish coat covering the intestine. This 

 is the so-called liver. 



(5) Remove the digestive tract, being careful not to 

 injure other structures. Just below will be seen the ventral 

 blood vessel already mentioned. 



(6) Scrape carefully the other loose tissue from the 

 floor of the body cavity, and below in the mid-ventral line 

 will be seen the white nerve cord. Remove the tissue from 

 it, tracing it forward, being careful not to break it. Now 

 place it under a dissecting microscope, still attached to the 

 body wall, and examine. Is it a single or a double cord? 

 Do you see enlargements along this cord? How many? 

 They are called ganglia. Are there any nerves arising from 

 them as side branches? Trace it further forward till you 

 find where it divides, forming a collar around the esophagus. 

 This is called the esophageal collar. Just where the cord 

 begins to divide is a large double ganglion, the infra-eso- 

 phageal ganglion. Above the esophagus, where the two 

 parts of the esophageal collar unite again, is the supra- 

 esophageal ganglion. It is double also. 



(7) You can also now see the nephridia, little white 

 coiled tubes between the septa. These are organs of excre- 

 tion. Study one and see if you can trace it in its windings. 



