ALIMENTAEY CANAL. 197 



the dorsal surface of the hmder end of the pharynx 



to the intestine. 

 d. The intestine is wider in front, and narrows behind, 



running back to the anus. 

 6. The liver is a large saccular diverticulum from the 



front end of the intestine, which extends forwards 



along the right side of the hinder two-thirds or 



more of the pharynx. 



To make out the relations of the pharynx, cesopliagus, and 

 intestine to one another, carefully remove the liver. 



11. The structure of the alimentary canal. 



a. The buccal tentacles. 



Remove the entire buccal skeleton, with the tentacles in 

 both sides, carefully dissecting it with needles from its attach- 

 ments. Stain it with picrocarmine ; mount on a slide in 

 glycerine, and examine icith the microscope. 



A jointed skeletal bar borders the buccal aper- 

 ture on each side, and supports the buccal ten- 

 tacles. 



b. The pharynx. 



Remove a portion of the pharynx carefully : divideit along 

 the mid-dorsal line, and spread it out fiat on a slide ; stain it ; 

 mount in glycerine, and examine with the microscope. 



The arrangement of the gill-arches and gill- 

 clefts, and their relation to the endostyle, can be 

 well made out. 



Retnove a second length of the pharynx, and with a fine 

 brush pencil off the epithelium from the gill-arches. Treat a 

 third portion with a solution of caustic potash. Mount in 

 glycerine, and examine with the microscope. 



The primary or spUt rods, and the secondary 

 or unsplit rods (compare p. 185), can be readily 

 made out ; also the horizontal bars connecting 

 the successive pairs of primary rods together, and 

 the relations of the rods to the endostyle. 



