Branch An nu lata 47 



IV. — A few segments back of the head find a ring-like 

 sweUing of the body : this is the clitellum. It is more 

 prominent in some specimens than in others. 



V. — Examine the external surface carefully for openings 



through the skin. The mouth and anal openings are 

 easily found. Find a small pore in the grooves between 

 successive segments behind the tenth along the mid- 

 dorsal line ; these communicate with the body cavity 

 and will sometimes emit a milky fluid when the animal 

 is irritated. On the ventral side of the fourteenth seg- 

 ment find two small openings, the external terminations 

 of ducts leading from the ovaries. The external open- 

 ings leading to the seminal vesicles will be found in the 

 fifteenth segment. Draw a side-view of the earthworm. 



INTERNAL ANATOMY 



VI. — Pin the specimen to the bottom of the dissecting 

 dish with its ventral surface downward, by inserting 

 one pin through the prostomium and another through 

 the posterior segment, stretching the body a little. 

 With sharp-pointed scissors cut through the very thin 

 body wall, near to and parallel with the dorsal median 

 hne. Be careful not to cut too deep. Notice the 

 many transverse partitions joined to the inner surface 

 of the body wall. Determine whether they correspond 

 to the constrictions between the segments. Cut these 

 partitions carefully down each side close to the body 

 wall, and pin down the flaps of skin thus laid open. 



II. — The alimentary canal is now exposed. Notice that 

 it passes directly through the partitions between the 

 segments. See the dorsal blood-vessel along the top 

 of the ahmentary canal. Near the eighth and ninth 

 segments, find branches running from this dorsal blood- 



