122 W. C. ALLEE. 



trie vessel which continues into the dorsally situated heart. From 

 the heart the branchial vessels go forward to the three pairs of 

 gills. Find the ventral vessel and note its transverse branches, 

 some of which encircle the digestive organs. You may be able 

 to see also the dorsal, neural, lateral and esophageal vessels, all 

 longitudinal . 



Digestive System. Is the mouth ventral or dorsal ? It leads 

 into the straight muscular esophagus. How is the latter held in 

 place? Is there a protrusible pharynx? The esophagus opens 

 into the wide straight stomach. Does it show any segmentation? 

 The winding portion of the alimentary tract is the intestine which 

 continues to the anus. Cut open the stomach and note the char- 

 acter of its walls. 



Muscles. Find the transverse-oblique, longitudinal, setal, and 

 circular muscles. Make a rough diagram of the animal through 

 the stomach region, showing the relative positions of the muscles, 

 stomach, and blood vessels. 



Nephridia. Cut through the oblique muscles in anterior so- 

 mites and expose the nephridia. Quickly sketch the natural po- 

 sition and shape of one of them. How many external openings 

 or nephridiopores do you find? Put a nephriclium from a freshly 

 killed worm under the microscope. How do you think the ne- 

 phridium functions in the living body? The gonadal glands are 

 small white glands ventral to the esophagus. Ventral to them 

 are the larger and yellowish " stomach glands." The nephridia 

 may serve as gonoducts. 



Nervous System. Displace the digestive organs to one side 

 and find the ventral nerve cord. Has it ganglia? Can you find 

 paired transverse branches? What features of the nervous sys- 

 tem are metameric? How far does the ventral nerve cord go 

 posteriorly? Anteriorly try to find the sub-esophageal ganglion, 

 the circum-esophageal connectives and the supra-esophageal 

 ganglion. Where would you expect to find sense organs in Am- 

 phitritef 



Make a list of the special features of the anatomy in Amphitrite 

 that are especially significant in view of its habit of living. Com- 

 pare the anatomy with that of Nereis. Which of the two species 



