MACROBDELLA. 105 



action is produced, and how the blood is forced into the stomach. 

 The cavity of the mouth will be studied later. 



Cut the digestive tract at the rectum and at about the middle 

 of the pharynx and carefully dissect it loose. 

 Beneath it notice : 



1. The nerve cord. Do the ganglia have any relation to 

 somites? Find the lateral nerves leaving them. Trace the con- 

 nectives between them. This will receive more attention later. 



2. The ventral blood-vessel and the lateral branches. 



3. The nephridia, of which there are eighteen pairs. 



4. The male reproductive organs. On the mid-ventral line 

 ventral to the nerve cord, and opposite the external opening 

 already observed, is the globular muscular penis. Just anterior 

 and laterally are a pair of white seminal vesicles. A short broad 

 duct leads from each vesicle to the penis and a long narrow duct 

 leads posteriorly to connect with the nine testes on the same 

 side. The anterior pair of testes are four somites behind the 

 penis and the eight others are in the succeeding somites. The 

 testes are rounded white organs near the nerve cord. 



Draw. 



5. The female reproductive organs lie behind the penis. 

 The vagina is a muscular sac on the median line opposite the 

 opening already described. 



From the anterior dorsal side the oviducts run to the two small 

 white ovaries, which are near the vagina, but a little anterior 

 and lateral to it. 



6. Behind the vagina opposite the openings on the ventral 

 side are the four mucous glands. 



Draw. 



7. Nervous System. The location of the ventral cord has 

 already been noticed. Find 



(a) The number of ganglia. 



(6) Whether the ganglia are of equal size? Do they all give 

 off the same number of lateral nerves? 



(c) The supra-esophageal ganglia, above the pharynx. 



