URO GENITAL SYSTEM. 353 



the interrenal tissue is on the outer side of the adrenal organ, the su- 

 prarenal forming the inner portion. In the amphibia the adrenals are 

 closely connected with the mesonephroi, being attached to their 

 inner margins (urodeles) or to the ventral surface (anura). In the 

 reptiles they are lobulated structures near the gonads. In the mammals 

 they are more compact (often called suprarenals) and are placed at the 

 anterior end of the kidneys, often unsymmetrically. 



Both organs are regarded as glands of internal secretion, their 

 product being passed directly into the blood. The secretion of the 

 medullary portion (suprarenal) of the mammals is adrenalin, an acti- 

 vator or hormone, which by its action on the muscular system causes 

 an increase in the blood pressure. Even less is known of the function 

 of the interrenal. Certain observations render it probable that the 

 secretion of this is of value in destroying certain products of metabolism 

 which otherwise might be injurious to the organism. 



