94 LABORATORY WORK. 



pear-shaped enlargement (pharynx) occupying about half a 

 dozen segments in front. Notice the muscle-fibres going 

 to the pharynx from the body-wall. (2) A narrower tube 

 (oesophagus) leading back through about ten segments 

 from the pharynx, and expanding, about segment 16, into 

 (3) a heart-shaped crop, which in turn is followed by (4) a 

 second enlargement (gizzard) of about the same size. 

 (5) 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 oesophagus 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 

 other parts 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) . 

 With what is ttue intestine filled? 



