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 esophagus 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 esophagus 
and contain calcareous crystals. The crop is a thin-walled dila- 
tion of the esophagus 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 soniites 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. 
Seyer 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 
