LUMBRICUS. 85 



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

 they 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 between 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 

 with your microscope. Notice that it consists of a coiled tube 

 of varying diameter. The funnel is not easy to find and is hard 

 to remove. It may be found by removing the portion of the 

 septum through which the nephridium passes and examining 

 it with a microscope. 



Draw the nephridia into your previous figure. 



Cut the stomach-intestine behind the gizzard and pull it 

 forward, carefully separating the tissue from it as it is drawn for- 

 ward, so underlying organs will not be disturbed. In this way 

 free the alimentary canal to the position of the pharynx. 



You can now see the extent of the nephridia, and possibly 

 see where they perforate the septa. 



