DISSECTION OF EARTHWORM. 23T 



From the gizzard the intestine can be traced back to the 

 vent. 



Lying above the alimentary tract is the dorsal blood- 

 vessel. From it are given off transverse vessels. Are 

 these in pairs ? Do they correspond to the segments in 

 number and position ? Are any of them enlarged ? In 

 what direction do they go ? Can you find (by tipping the 

 alimentary canal) a ventral blood-vessel beneath ? Do any 

 vessels connect with it ? 



On the top of the anterior end of the oesophagus are two 

 pear-shaped bodies, the brain. Can you find nerve-cords 

 (commissures) leading downward and backward from the 

 brain ? 



Arising from either side and extending upwards so as 

 to overlap the esophagus above are lobes of the repro- 

 ductive organs. Draw the parts so far made out, viewed 

 from above, and then cut through the pharynx and care- 

 fully lift up the alimentary canal as far back as the be- 

 ginning of the intestine, cutting it off at that point. Now 

 sketch the reproductive organs, lifting them up to see if 

 any organs occur beneath. 



Examine the cut end of the intestine. Is the inside a 

 circular tube ? On the dorsal surface of the intestine see 

 the dark green chloragogue organ (a digestive gland, sup- 

 posed to be something like liver or pancreas in its action). 



On the middle line of the floor of the body find the 

 ventral nerve-cord, with its numerous enlargements (gan- 

 glia). Are these latter equal in number to the somites ? 

 Do they occur in or between the somites ? Trace the 

 nervous system forwards, and find out how it Connects with 

 the brain. Draw the brain and twenty ganglia of the ven- 

 tral chain connected together. Just outside the ventral 

 nervous cord find in each segment (except a few anterior) 



