SlO Royal Society. 



scribed by Mviller. The epithelium lining the uriniferous tube is 

 altered in its character where the tube is continuous with the cap- 

 sule, being there more transparent, and furnished with cilia, which, 

 in the frog, may be seen, for manj' hours after death, in very active 

 motion, directing a current down the tube. Farther within the cap- 

 sule the epithelium is excessively delicate, and even, in many cases, 

 absent. The renal artery, with the exception of a few branches given 

 off to the capsule, surrounding fat, and coats of the larger blood- 

 vessels, divides itself into minute twigs, Avliich are the afferent ves- 

 sels of the Malpighian tufts. After it has pierced the capsule, the 

 twig dilates, and suddenly divides and subdivides itself into several 

 minute branches, terminating in convoluted capillaries, which are 

 collected in the form of a ball ; and from the interior of the ball the 

 solitary efferent vessel emerges, passing out of the capsule by the 

 side of the single afferent vessel. This ball lies loose and bare in 

 the capsule, being attached to it only by its afferent and efferent ves- 

 sel ; and is divided into as many lobes as there are primary subdivi- 

 sions of the afferent vessel ; and every vessel composing it is bare and 

 uncovered, an arrangement of which the economy presents no other 

 example. The eifei-ent vessels, on leaving the Malpighian bodies, 

 enter separately the plexus of capillaries surrounding the uriniferous 

 tubes, and supply that plexus with blood. The blood of the vasa 

 vasorum also probably enters this plexus. The plexus itself lies on 

 the outside of the tubes, on the deep sui'face of the membrane which 

 furnishes the secretion ; and from it the renal vein arises by nume- 

 rous radicles. 



Thus the blood, in its course through the kidney, passes through 

 two distinct systems of capillary vessels ; first, through that within 

 the extremities of the uriniferous tubes; and secondly, through that 

 on the exterior of these tubes. The author points out striking dif- 

 ferences between these two systems. He also describes collectively 

 under the name of Portal System of the Kidneij, all the solitary ef- 

 ferent vessels of the Malpighian bodies, and compares them with 

 the portal system of the liver ; botli serving to convey blood between 

 two capillary systems. In the latter, a trunk is formed merely for the 

 convenience of transport, the two systems it connects being far apart. 

 But a portion even of this has no venous trunk, viz. that furnished 

 by the capillaries of the hepatic artery throughout the liver, which 

 pour themselves either into the terminal branches of the portal vein, 

 or else directly into the portal-hepatic capillary plexus. On the other 

 hand, in the kidney, the efferent vessels of the Malpighian bodies, 

 situated near the medullary cones, having to supply the plexus of 

 the cones, which is at some little distance, ai-e often large, and divide 

 themselves after the manner of an artery. They are portal veins in 

 miniature. In further confinnation of his view of the existence of a 

 true portal system in the kidney of the higher orders of animals, 

 where it has never hitherto been suspected, the author describes his 

 observations on the circulation through the kidney of the Boa Con- 

 strictor, an animal which affords a good example of those in which 

 portal blood derived from the hinder part of the body traverses 

 the kidney. He shows that here the Malpighian bodies are sup- 



