76 ANNELIDA. 



the pharynx. Through how many somites does this extend ? It is 

 connected with the body-wall by numerous, radiating muscle 

 fibers. What function do these fibers perform ? 



2. Behind the pharynx is the narrow and long esophagus. 

 This runs posteriorly between lobed, light colored organs, the 

 seminal vesicles, that will be studied in connection with the 

 reproductive organs. Press these aside and notice the small 

 calciferous glands. 



3. The esophagus leads to the crop, which lies just anterior 

 to and in contact with the gizzard. In what somites are 

 these organs placed ? What is their shape ? Do you understand 

 the function of each? 



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 j^ou find other vessels 

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

 they placed ? Do they appear like the aortic arches ? 



Make a draimng 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 



