134 WORMS. 



with the depressions between segments seen on the exte- 

 rior, and show internal segmentation. Observe that each 

 of the septa is perforated at the center for the passage of 

 the alimentary canal and other vessels. Observe, also, 

 that the segmentation of the body extends to the alimen- 

 tary canal, which in this region is somewhat expanded in 

 each segment. 



Beginning at the anterior end, cut the septa close to the 

 body wall on each side down to the uppermost row of 

 setae, and pin back the flaps, exposing the internal organs. 

 Most conspicuous among these will be the large-lobed, 

 white seminal vesicles, nearly filling the body cavity 

 between the tenth and the fifteenth segments, and 

 the darker-colored alimentary canal extending straight 

 through the center of the body longitudinally. 



Find a dorsal Hood vessel extended along the upper side 

 of the alimentary canal, with five pairs of aortic arches 

 extending downward from it in segments 7 to 11, and 

 meeting below the alimentary canal in the ventral blood 

 vessel, which extends backwards longitudinally. 



I. Organs of Digestion. Beginning at the posterior 

 end, lift out the alimentary canal, carefully dissecting it 

 free from the septa, and avoiding disturbing other organs. 

 Make out in the alimentary canal the following parts : 



1. A wide pharynx, posterior to the mouth, with many 

 radiating muscle fibers extending from its walls to the 

 outer body walls. When the soft margins of the mouth 

 are applied to any object that is to be seized, these muscle 

 fibers, contracting, dilate the pharynx, creating within it 

 a partial vacuum, and exerting a powerful sucking action 

 upon the object seized. 



2. An esophagus, a slender, thin-walled tube, extending 

 backward from the pharynx. 



3. Three pairs of minute yellowish white calciferous 

 glands attached to the esophagus in segments 10 to 12. 



