THE RENAL VESSELS IN ANIMALS. 789 



The kidneys in Birds, Eeptiles, Amphibia, and Fishes, may be considered 

 as composed entirely of cortical substance ; they invariably contain Malpighian 

 corpuscles, or arterial glomeruli, which are usually scattered through the gland, 

 and, as usual, project into dilatations of the uriniferous tubuli. These bodies 

 vary in size, apparently in accordance with the size of the animal, as well as 

 in different Classes. Thus they are larger, ^ and J rj of an inch, in the lion and 

 horse, than in Man, T J n ; they are much smaller in the guinea-pig, cat, and 

 mouse, s4o to F: , T of an inch ; they are small in Fishes, 5 ,} ff , and Amphibia, z , 

 but smallest of all in Reptiles, F | ff to ? i ff . In the pointed renal lobules of the 

 boa, they are smaller in the narrow than in the wider portions of each lobule. 

 In the simpler kidneys of Fishes, they are represented by small vascular plex- 

 uses. Cilia are found in the uriniferous tubuli in the Cold-blooded Vertebrata ; 

 they commence at the neck of the capsules into which the Malpighian bodies 

 project, and extend for a short distance along the tubuli, sometimes through- 

 put their whole length. The current which they produce as seen after death, 

 is towards the orifices of the tubules. Cilia have not yet been distinctly seen 

 in Birds or Mammalia. 



In Birds, Reptiles, Amphibia, and Fishes, the renal arteries, instead of being 

 two in number as in Mammalia, are numerous, and are derived from adjacent 

 branches of the aorta, or from the aorta itself. Besides this, the kidneys in 

 these Classes, receive more or less venous blood from the hinder limbs in Birds 

 and the four-footed Reptiles and Amphibia, and from the hinder parts of the 

 body in Ophidia and in Fishes. The rest of the blood from the hinder portion 

 of the body, usually passes partly to the vena cava, and partly to the vena 

 portse ; in Reptiles, Amphibia, and most Fishes, it goes chiefly to the latter ; 

 in a few Fishes all the blood from the hinder part of the body proceeds to the 

 kidneys. 



The fact that the kidneys in Birds, Reptiles, Amphibia, and Fishes, receive 

 a supply of venous blood was first noticed by Bojanus, but the detailed arrange- 

 ment of the afferent veins was fully investigated by Jacobson. These renal 

 portal veins become more numerous in the lower Vertebrata. After entering 

 the kidneys, they quickly subdivide, and end in the vascular plexuses which 

 surround the uriniferous tubuli. The Malpighian bodies still receive arterial 

 vessels only, but give off efferent vessels which join the plexuses around the 

 tubuli. In the lower Vertebrata, accordingly, the special urinary products, 

 like the bile products, are, in all cases, excreted from venous blood ; and the 

 small quantity of arterial blood which enters the kidneys, first passes through 

 the vascular tufts of the Malpighian bodies, and so becomes modified, before 

 it reaches the plexuses around the proper excreting tubuli, in the same manner 

 that the hepatic arterial blood becomes venous, before it reaches the intra-lob- 

 ular plexuses of the liver. As already stated, the existence of this portal ar- 

 rangement of the vessels in the kidneys of Birds, Reptiles, Amphibia, and 

 Fishes, supports the view, that in Mammalia, also, the renal arterial blood 

 becomes venous in traversing the vessels of the glomeruli, before it serves for 

 the excretion of urinary constituents. The pasty or solid character of the 

 urine in Serpents, may depend, not only on the small size of the glomeruli, but 

 also on the fact that these animals swallow little or no water. 



Excretory glandular organs, having the function of kidneys, exist at least 

 in the higher Non-vertebrate animals ; but owing to the different plans of con- 

 struction in these Subkingdoms, it is impossible to recognize much, if any, 

 resemblance of position or structure, between them and the renal organs even 

 of the lowest Fishes. But the unity of the vito-chemical processes of animal 

 life, is proved by the detection of urinary products in some of these excretory 

 organs in the Mollusca, Annulosa, and Ccelenterata. Uric acid has been found 

 in the two former Classes, and guanin in the last. 



In the Mollusca, the organs which represent kidneys are not connected by 

 ducts with the alimentary canal. In the Cephalopods, remarkable spongy 

 masses of follicles exist around the large branchial veins, and discharge them- 

 selves, by numerous- aperture^ into the branchial cavity ; these are supposed to 

 act as renal emunctory organs,, their excreted fluid containing uric acid. In 

 the Gasteropods, a smaller follicular organ, also containing that acid, is usu- 

 ally found in the neighborhood of the heart, and its ducts open near the intes- 



