BLOOD 455 



processes occur when the temperature rises. In some mammals, 

 notably man, the sweat glands are also important, particularly 

 at high temperatures, when they produce much water which 

 takes much heat from the body by evaporation. In others, such 

 as the dog, panting helps to prevent the body temperature from 

 rising. A rapid intake of air into the mouth but not the lungs 

 causes increased evaporation from its moist surface. 



EXCRETORY ORGANS 



The kidneys of the rabbit are a pair of dark-red bodies, 

 convex on the outer side and concave on the inner, which 

 lie on the dorsal wall of the peritoneal cavity, that on the 

 left side farther back than that on the right. Like those of the 

 dogfish and frog they consist of tubules, but these even in the 

 embryo do not open into the peritoneal cavity. Each begins 

 as a Bowman's capsule (Fig. 295), which contains a small part 

 of the coelom, and has pushed into one side of it the glomerulus, 

 a cluster of blood vessels supplied from the renal artery. Capsule 

 and glomerulus are known as the Malpighian body. From the 

 capsule there leads away the tubule. The tubules join together 

 into collecting ducts, and finally open into the ureter, a duct 

 which has no counterpart in dogfish or frog. From the concavity 

 or hilus of the kidney the ureter runs back to open into the bladder. 

 In the early stages of development this organ joins the rectum 

 in a cloaca, but later the latter becomes divided, so that excretory 

 and faecal products are not mixed. The opening of the bladder 

 is different in the two sexes and is described below. The principal 

 excretory product is urea, which is separated from the blood in the 

 glomerulus, and much water is reabsorbed in the tubule. 



REPRODUCTION 



The testes (Fig. 359) are a pair of ovoid bodies which arise 

 in the course of development on the dorsal wall of the peritoneal 

 cavity near the kidney, but later become free and pass backward 

 through the inguinal canals into two pouches of the body-wall 

 at the sides of the penis known as the scrotal sacs. Each testis 

 remains connected with its original position by a spermatic 

 cord, which consists of connective tissue with an artery, vein, 

 and nerve. In passing backwards it carries with it a part of the 



