MACROBDELLA. 105 



latter are arranged in conspicuous bundles. Lining the body- 

 wall is the thin peritoneal layer. Do you understand the func- 

 tion of each of these layers? How is the body elongated? 



3. Find the set(B and determine where they are placed, ho'W 

 many are in each group, how many groups there are, how they 

 pierce the body-wall, and what muscles are attached to them. 

 Why are setae not in every section? 



4. The alimentary canal consists of a lining epithelium, 

 followed by connective tissue and muscle, and, on its outer wall, 

 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 hlood-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 fcetida. Am. Jour. Physiol., 4, 1901. 

 Sedgewick 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. 



