MACROBDELLA. 107 



trally. Determine its shape. The mouth with the region 

 around it forms a sucker. 



2. The male reproductive aperture on the median ventral 

 portion of the thirtieth riYig. This is surrounded by a thicken- 

 ing. 



3. The female reproductive aperture on the median hne at 

 the posterior margin of the thirty-fifth ring. This is not marked 

 by a distinct thickening. 



4. Four apertures with thickened margins arranged in the 

 form of a square between the thirty-ninth and fortieth and 

 fortieth and forty-first rings. These are the apertures of the 

 mucous glands. 



5. The external apertures of the nephridia about half-way 

 between the median fine and the margins, on the posterior edge 

 of the last ring of a somite. The spots are light colored and 

 elliptical. These are important landmarks in determining 

 the boundaries of somites. Some of the anterior and posterior 

 somites do not bear them. 



6. The posterior sucker. Its size, shape, and structure. 



Preserved specimens if very hard should be placed in water 

 some time before dissection. Cut through the body wall along 

 the mid-dorsal line, being careful not to cut underlying organs. 

 Lift up the flap of integument and cut the connective tissue 

 loose so it may be turned and pinned back under water. Work 

 forward and backward from the middle of the back. 



1. The digestive tract consists of a buccal pouch, pharynx, 

 stomach, and intestine. 



2. The pharynx is thick walled, elongated, and bound to the 

 body wall by radiating muscle-fibers. What is their function? 

 The pharynx is muscular and is provided with bands of longi- 

 tudinal and with circular muscles. What function is performed 

 by these fibers? 



3. The stomach joins the pharynx, is large, and has divertic- 

 ula that nearly fill the body cavity. It occupies a considerable 

 portion of the length of the body. How many pouches has it? 



