616 PROCEEDINGS OF THE AMERICAN ACADEMY. 



terior to the origin of the esophagus. Each gland is flask-shaped, the 

 neck of the flask being only one half the diameter of its fundus. These 

 glands are partly covered by the nerve collar. In the wall of the buc- 

 cal tube there are a considerable number of smaU glands that open 

 into the buccal cavity. 



3. Histology of Digestive System. 



The walls of the buccal cavity, the pharynx, and the suctorial bulb 

 are lined with a firm, thin layer of chitin, which is as deeply colored as 

 the first row of lateral teeth. In the suctorial bulb and the posterior 

 region of the pharynx the chitin is thinner and less deeply colored. 



The esophagus is lined for its entire length with a ciliated epithe- 

 lium, which makes up about one half of the thickness of the wall, the 

 remaining portion being made up of connective-tissue and muscle cells. 



The wall of the stomach-intestine is composed of a thick inner epi- 

 thelial layer, with a well marked basement membrane, and a very thin 

 outer layer of muscle and connective tissue, which in many places is 

 only one or two cells thick. The cells in the epithelial layer are large, 

 but from the basement membrane to the free surface the distance is 

 noticeably short. The free end of each cell is highly vacuolated ; the 

 nucleus is basal and surrounded by fine cytoplasmic granules. These 

 cells show little variation in their appearance throughout the length of 

 the stomach-intestine. 



The cells of the salivary glands are quite uniform in size, possibly a 

 little longer in the larger part of the gland. Each cell is nearly cylin- 

 drical ; its nucleus is basal, and its cytoplasm finely and homogeneously 

 granular. 



4. The Liver. 



The liver occupies more than one half of the posterior visceral mass ; 

 its anterior two-thirds is surrounded by the hermaphroditic gland (see 

 infra), which extends inward some distance, though the liver lobules, 

 lying between the germinal follicles, extend in many places to the sur- 

 face. The posterior third of the visceral mass is composed entirely of 

 the liver, which is made up of numerous racemose lobes, giving it a 

 rather loose appearance. The lobules of the liver open by minute 

 connecting ducts into one or the other of the two bile sacs, the greater 

 number opening into the posterior one, which is much the larger. 



The cells are stained brown in Hermann's fluid, owing to the action 

 of the osmic acid on the granules surrounding the numerous, rather 

 large vacuoles contained in each cell. The free ends of the liver cells 

 are irregular in outline and the cavity of the lobe, which in the granu- 



