SEGMENTED WORMS— THE ANNELIDS 



175 



more limited, but if you have ever watched a chicken hop around after 

 its head had been chopped off you surely know that these reflexes are 

 found in more advanced animals. However, there is nothing like the 

 giant fibers to give the coordination found in the earthworm. 



Reproduction in the earthworms is very interesting. They are her- 

 maphroditic, but have copulation with a mutual exchange of sperms in a 

 manner that is somewhat similar to that in planaria. The testes are 

 contained within the large seminal vesicles that extend from segments 

 nine to thirteen and the two vasa deferentia lead back from these to a 

 pair of external openings in segment fifteen. The female organs consist 

 of a pair of ovaries in segment thirteen, a pair of oviducts which open 



Courtesy General Biological Supply House 



Fig. 12.4. Copulating earthworms. This picture was made outdoors on a rainy night 



by flashgun. 



in segment fourteen, and two pairs of seminal receptacles in segments 

 nine and ten. 



During copulation two worms come together facing in opposite 

 directions with their ventral surfaces in contact. The anterior ends of 

 their bodies become fused together by a layer of mucous secretions so 

 that the openings of their sex ducts are fairly close together. Sperms 

 are discharged from the openings of the vasa deferentia, and pass down 

 two pairs of grooves in the slime until they come to the openings of 

 the seminal receptacles which they enter. It is a mutual exchange with 

 each worm receiving sperms from the other. When insemination is 

 completed the worms separate. 



Later a swollen, band-like portion of the body, called the clitellum, 

 which occupies segments 32 to 37, secretes a series of cocoons. Each 

 cocoon slides over the anterior end of the earthworm and, as it passes 

 the openings of the oviducts, eggs are laid in it. Then, as it passes the 



