STRUCTURE AND FUNCTION 65 



Definitions. 



Body cavity, the space between the body wall and the 

 alimentary canal. 



Septa (singular, septum), the thin walls between somites, 

 seen when the worm is opened. 



Pharynx, the hard-walled, rather bulbous, anterior por- 

 tion of the alimentary canal. 



Esophagus, the portion of the alimentary canal extending 

 back from the pharynx with thinner walls and smaller 

 diameter. 



Crop, the short, wide portion of the canal back of the 

 esophagus. 



Gizzard, the hard- walled, short region, just back of the 

 crop. 



Stomach-intestine, the portion of the canal reaching from 

 the gizzard to the anus. 



Ventral nerve cord, a light-colored thread lying against 

 the inner surface of the ventral body wall. 



Nerve ganglia (singula.!, ganglion), slight swellings on 

 the ventral nerve cord. 



Nerve ring or collar, a pair of nerves extending from the 

 ventral nerve cord around the pharynx to a pair of ganglia 

 (often called the "brain") in the dorsal region of the 

 anterior end. 



Kidney tubes or nephridia, the excretory organs of the 

 earthworm, occurring as slender, paired tubes in nearly 

 every somite. 



Directions. 



Select a large worm and cut carefully through the body 

 wall along one side, midway between the dorsal and ventral 

 surfaces, from the anterior end to the posterior. Lay the 

 worm on any convenient fairly soft surface (a piece of 



