102 ANNELIDA. 



peritoneal cells, which in the region of the stomach-intestine 

 are large, very numerous, and are known as the chloragog cells. 



5. Lying in the mid-ventral line, beneath the alimentary 

 canal and close to the body-wall, is the ventral nerve cord. 

 Examine its structure. See if any of the sections show nerves 

 leaving it. 



6. Dorsal to the alimentary canal is the dorsal blood-vessel, on 

 its ventral side is the ventral blood-vessel, and ventral to the nerve 

 cord the sub-neural vessel. 



7. Find sections of the nephridia. Where are they placed? 

 How do the sections appear? Why? 



Other organs will appear in most of the sections. See if you 

 can identify them. 



Draw an enlarged cross-section. 



Darwin: The Formation of Vegetable Mold through the Action of Worms. 



Appleton and Co., 1888. 

 Harrington: The Calciferous Glands of the Earthworm, with Appendix on 



the Circulation. Jour. Morph., 15, 1899. 

 Parker and Arkin: The Directive Influence of Light on the Earthworm, 



Allolobophora foetida. Am. Jour. Physiol., 4, 1901. 

 Sedgewiek and Wilson : General Biology. 

 Wilson: the Embryology of the Earthworm. Jour. Morph., 3, 1889. 



MACROBDELLA. (Leech.) 



If you have living specimens notice their methods of loco- 

 motion both in crawling around the dish and in swimming. 

 A considerable volume of water is usually necessary to get the 

 animals to swim. 



Specimens may be killed with chloroform, narcotizing ma- 

 terials, or killing agents, such as weak chromic acid. 



Notice: 



1. The shape of the body. Which is the anterior end? 



2. Do the dorsal and ventral surfaces differ in shape and 

 color? 



3. The rings which encircle the body. Determine their 

 number. There is good evidence that these do not represent 

 somites. The somites are fewer in number and each is composed 

 .of from one to five of these rings. 



