102 ANNELIDA. 



4. Leaving the gizzard is the stomach-intestine, which runs 

 through the remainder of the body, giving off lateral diverticula 

 in each somite. Do you know its function? 



Notice the relation of the septa to the alimentary canal. 



Circulatory System. — 1. Lying dorsal to the alimentary 

 canal is the blood-vessel that could be seen pulsating in the 

 living specimen. In most cases this vessel is full of blood and 

 appears brown. 



2. Near the anterior end of the body large side branches, 

 the aortic arches, are given off on either side and pass down 

 around the esophagus. How many aortic arches do you find? 

 In what somites are they placed? ' 



3. Examine with a lens and see whether you find other vessels 

 connected with the dorsal aorta. If you do, determine how 

 they are placed. Do they appear like the aortic arches? 



Make a drawing of the anterior end of the body, showing the 

 points you have seen. 



4. Gently press the stomach-intestine to one side and see if 

 you find a blood-vessel beneath it. Do the aortic arches join 

 this? Other connections between blood-vessels are too small to 

 be studied in dissections, but you should understand from text- 

 books or lectures what they are, and the probable course of cir- 

 culation. 



Excretory System. — 1. A pair of nephridia occurs in each 

 somite, one nephridium on either side of the alimentary canal. 

 (The first three or four somites are not provided with nephridia.) 

 Each nephridium is a coiled tube, appearing to the unaided 

 eye as a fluffy mass, that opens externally betweec the groups 

 of setae, in the position already observed, and internally by a 

 small opening, the funnel. The inner opening is not in the 

 somite in which the most of the tube lies, but in the somite 

 anterior to it. That is, the nephridium that occupies the space 

 in somite twenty, opens externally on somite twenty, but in- 

 ternally perforates the septum directly anterior and opens into 

 somite nineteen. 



2. Remove a nephridium with your forceps and examine it 



