LUMBRICUS, MACROBDELLA 115 



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. 



1. Observe the shape of the body. Which is the anterior 

 end? 



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

 color? 



3. Note the rings which encircle the body. Determine 

 their number. There is good evidence that these do not rep- 

 resent somites. The somites are fewer in number and each 

 is composed of from one to five of these rings. 



On the dorsal surface: 



1. Near the anterior end is a series of ten small black 

 spots arranged in the form of a horseshoe with the arched 

 end forward. These are the eyes. They are arranged in 

 pairs on the first, second, third, fifth, and eighth rings. These 

 are believed to be on the first five somites. The first and 

 second somites comprise a single ring each; the third in- 

 cludes the third and fourth rings; the fourth — the fifth, sixth, 

 and seventh rings; the fifth — the eighth, ninth, and tenth 

 rings. 



2. Near the lateral edges notice the black pigment spots. 

 The larger spots are situated mostly on a single ring, but 

 may be extended on to others. Smaller pigment spots may 

 occur on other rings along the same line. There is evidence 

 that these larger spots mark the anterior rings of each somite 

 wherever they occur. How many rings are commonly in- 

 cluded in a somite? 



