326 EXCRETION 



Malpighian bodies. These are simply flask-like terminal dilatations of 

 the tubes themselves (see Plate VII, Fig. 4). 



The cortical portion of the kidney presents a delicate fibrous matrix, 

 which forms a support for the secreting portion and its bloodvessels. 

 The tubes of the cortical substance present considerable differences in 

 size, and three well-defined varieties can be distinguished : 



i. The first convoluted tubes, directly connected with the Mal- 

 pighian bodies. 2. Small tubes, continuous with the convoluted tubes, 

 dipping down into the pyramids and returning to the cortical portion 

 in the form of loops. 3. The second convoluted tubes, forming a plexus 

 connecting the different kinds of tubes with each other and finally with 

 the straight tubes of the pyramidal portion. 



In tracing out the course of the tubes, it will be found most con- 

 venient to begin with a description of the. Malpighian bodies and to 

 follow the tubes from these bodies to their connections with the straight 

 tubes of the pyramidal substance. 



Malpighian Bodies. These are ovoid or rounded terminal dilatations 

 of the first convoluted tubes and are ^\- to T -J-^ of an inch (100 to 250 /-t) 

 in diameter. They are composed of a membrane, which is continuous 

 with the external membrane of the convoluted tubes, and is of the same 

 homogeneous character, but somewhat thicker. This envelope, called 

 the capsule of Miiller or of Bowman, encloses a mass of convoluted 

 bloodvessels and is lined with a layer of nucleated epithelial cells. In 

 addition to the cells lining the capsule, there are other cells, which are 

 applied to the bloodvessels. 



The cells attached to the capsule of Miiller are smaller and more 

 transparent than those lining the convoluted tubes. They are ovoid, 

 nucleated and finely granular. The cells covering the vessels, however, 

 are larger and more opaque, and they resemble the epithelium lining 

 the tubes. They measure y^Vo to ToVo of an inch (16 to 25 /*,) in 

 diameter, by about ^Vo of an mcl1 ( IO ^) in thickness. 



Tubes of the Cortical Substance. Passing from the Malpighian 

 bodies the tubes present first a short constricted portion, called the 

 neck of the capsule, which soon dilates to the diameter of about ^^ of 

 an inch (50 /A), when their course becomes quite intricate and convoluted. 

 These are what are known as the first convoluted tubes. The mem- 

 brane of these tubes is transparent and homogeneous, but quite firm 

 and resisting. It is lined throughout with a single layer of epithelial 

 cells, T ^o- to ^Vo of an inch (16 to 25 /*) in diameter, somewhat larger, 

 therefore, than the cells lining the straight tubes. The cells lining the 

 convoluted tubes present two tolerably distinct portions. The inner 

 portion or zone, which is next the lumen of the tube, is finely granular, 



