ao(5 ELEMENTARY BIOLOGY. [CHAP. 



ment to the intestine; the blood-vessels run- 



mg in it. 



b. Divide the oesophagus close to the stomach and 

 the rectum near the cloaca: remove all the por- 

 tion of alimentary canal between these two 

 points, cutting through the mesentery. 



a. Pass a probe up the oesophagus into the mouth. 



/3. Open the upper end of the intestine and snip 

 off a bit of its internal layer (mucous mem- 

 brane) and mount in normal saline solution : 

 examine with |- obj.; on the fragment will be 

 found minute prominences (representing the 

 villi of the higher animals) covered by a closely- 

 set layer of cells (epithelium}. 



9. The kidneys. These organs are now exposed as two 

 elongated deep red bodies lying in the posterior 

 part of the perivisceral space close to the verte- 

 bral column; clear away any bits of mesentery, &c. 

 which may cover them; note 



a. The duct ureter (female) or genito-urinary canal 

 (male) running from the outer side of the pos- 

 terior part of each kidney to the cloaca. Open 

 the cloaca and pass a bristle into the opening of 

 one of the ureters. 



b. In the male R. esculenta each duct is somewhat 

 dilated after leaving the kidney : it then narrows 

 again and opens on the posterior surface of the 

 cloaca by an oblique slit with sharply defined 

 edges. In R. temporaria the duct does not 

 dilate, or only very slightly; but on its outer 

 side lies a glandular mass (vcsicula seminal is], 



