URINARY AND REPRODUCTIVE SYSTEMS 325 



In both sexes alike, the metanephros and its duct become 

 the kidney and ureter respectively. 



The bladder of the rabbit arises as a ventral diverticuluni 

 of the rectum, and is at first entirely independent of the 

 kidney-ducts, which open into the dorsal wall of the rectum, 

 a condition retained throughout life in the frog. During 

 development the ducts shift round so as to open into the 

 bladder, which then separates from the rectum and acquires 

 a separate opening to the exterior, through which the urinary 

 and genital products leave the body. 



It is convenient to describe the two sexes separately, as 

 they differ very greatly ; and to include in the account certain 

 glands in the neighbourhood of the rectum. 



A. The Male Rabbit. 

 1. The urinary system. 



a, The kidneys are a pair of dark-red bodies about an 

 inch and a quarter long, imbedded in fat in the 

 dorsal wall of the abdomen, outside the peri- 

 toneum. Each is of a flattened ovoid shape, with 

 a notch, the hilus, on its inner side where the 

 ureter and blood-vessels enter and leave it. 



Bisect one of the kidneys longitudinally, from its outer 

 edge : turn the ventral half inwards, so as to expose the cm 

 surfaces. 



i. The cortical substance forms the superficial 

 layer of the kidney : the Malpighian bodies, 

 which are confined to it, give it a dotted 

 appearance. 



ii. The medullary substance, forming the deeper 

 part of the kidney, is radially striated, and 

 consists mainly of the non-glandular parts of 

 the tubules. The inner surface of the medul- 

 lary substance is raised into a number of conical 

 papilla? or pyramids, on which the tubules open, 

 iii. The pelvis is the expanded anterior end of the 

 ureter, which lies in the cavity of the kidney, 



