n8 



ANIMAL BIOLOGY 



The earthworm's nervous system consists of a small 

 brain over the pharynx, connected by commissures with a 

 double chain of ganglia extending along the ventral side 

 of the body, there being in each segment a single pair of 

 ganglia which supply the adjacent parts with nerves. 

 While earthworms have no well-defined eyes, they are 

 very sensitive to light and tend to keep in dark situations. 



organs 



n.c 



FIG. 100. A few segments of the earthworm with the dorsal side cut 

 away and showing the intestine cut through, bv, blood vessels; d, dorsal 

 blood vessel; i, intestine; n.c., nerve cord; s, septa; ty, typhlosole or fold 

 projecting into the dorsal side of the intestine; v, ventral blood vessel. 

 (After Hatschek and Cori.) 



They will crawl away from the light; and when light is 

 flashed on them at night when they are partly outside of 

 their burrows they very quickly withdraw. Earthworms 

 are very sensitive to chemical and mechanical stimulation. 

 A slight jar may cause them to retreat quickly into their 

 burrows. 



The reproductive system of earthworms is very complex. 

 Both male and female organs are located in the same in- 

 dividual but the eggs are nevertheless generally fertilized 

 by sperm derived from another worm. The eggs are 



