DIGESTIVE SYSTEM. 127 



Insert one blade of a pair of scissors into the pulmonary 

 aperture from the outside, and cut through the collar, keeping 

 close to the left side of the aperture. Turn the right lip of 

 the aperture over to the right side. Pass a seeker into the rectum 

 from the anus so as to identify it. Note the ureter running 

 along the right side of the rectum, but dorsal to it in the natural 

 position of the parts. Trace the ureter forwards to its opening, 

 and inflate it with a blowpipe. Insert a seeker into the opening, 

 and, using this as a guide, slit up the ureter along its whole 

 length, following it back to the hinder end of the mantle-cavity, 

 and then forwards close alongside the kidney to its anterior 

 end, into which it opens. 



3. The rectum is a wide tube running along the right side 

 of the mantle-cavity, ventral to the ureter. It opens 

 in front at the anus, which has already been seen. 



Insert a bristle or seeker into the rectum from the anus, 

 and note carefully the relations of the anus and the respira- 

 tory and renal apertures. 



III. DISSECTION OF THE DIGESTIVE SYSTEM. 



Cut away the part of the collar to the left of the pulmo- 

 nary aperture. Detach the right side of the collar, with the anal 

 aperture, from the body-wall. Separate the rectum from the 

 body by cutting along the right side of the mantle, just below 

 the rectum, as far back as the hinder end of the mantle-cavity. 

 Turn the rectum back, and pin it down. 



Make a median longitudinal incision through the floor of 

 the mantle-cavity, and continue it forwards along the head to 

 its anterior end. Dissect the flaps away from the underlying 

 parts, and pin them out right and left. 



Carefully remove the thin skin covering the spiral visceral 

 mass, and unravel the reproductive organs, which are white 

 in colour and very bulky, and the alimentary canal, the coils 

 of which are very intimately connected with the liver. 



Arrange the reproductive organs on the right, the digestive 

 organs on the left side of the dissection. 



