AN EARTHWORM 71 



cases, pass directly between the longitudinal vessels, but break 

 into capillaries between them. 



The digestive system. The pharynx is an oval, muscular pouch 

 occupying somites 2 to 6 ; radiating muscle fibers join it with 

 the body- wall. The oesophagus is a slender tube occupying 

 somites 7 to 14 and running between the conspicuous sperm- 

 sacs. Press aside these sacs and notice beneath them three pairs 

 of white glands ; these are lateral diverticula of the oesophagus 

 and contain calcareous crystals. The crop is a thin-walled dila- 

 tion of the oesophagus which lies in somites 15 and 16. The 

 gizzard is a muscular, thick-walled chamber of the same size as the 

 crop and lying in somites 17 to 19. The stomach-intestine is a 

 large tube with lateral segmental pouches, which passes to the 

 hinder end of the body; covering the surface of the stomach- 

 intestine is a loose mass of yellowish brown cells, the chloragogue 

 cells, whose function is probably excretory. 



Exercise 3. Make a drawing of the opened animal on a scale of 

 3, showing the segmentation and representing the organs 

 above described in their proper somites; label all care- 

 fully. 



Sever the alimentary tract just back of the pharynx and 

 remove it from the body. 



The reproductive system. The earthworm is hermaphroditic 

 and possesses the following genital organs : 



The male organs. 1. The sperm-sacs have already been noticed. 

 They are large, white, irregularly lobed sacs occupying somites 

 9 to 13 ; they vary in size with the sexual condition of the 

 animal, being largest during periods of sexual activity. 2. The 

 testes. Two pairs of these organs are present, which lie beneath 

 the sperm-sacs in the tenth and eleventh somites ; they are very 

 minute objects and will be seen with difficulty, if at all. Push 

 aside the sperm-sacs and look for them with the aid of a hand 

 lens. 3. The sperm-ducts. These are slender tubes which begin 



