PHASCOLOSOMA 121 



supra- esophageal ganglion. The ganglion is small and situ- 

 ated behind the crown of tentacles, to which sensory nerves 

 extend. Does any system of organs show segmentation? 

 Make a drawing to show the internal anatomy. 



Adolph: Some Physiological Distinctions between Fresh-water and 



Marine Organisms. Biol. Bull., 48, 1925. 

 Gerould: The Development of Phascolosoma. Zool. Jahrb., 23, 1906. 

 Wilson, C. B.: Our North American Echiurids. Biol. Bull., 1, 1900. 



