428 THE SOLIDS. 



dular or secretory, which is the most important and charac- 

 teristic ; and the vascular, which is but subordinate. 



Secreting Apparatus. 



The secreting apparatus of 4he kidney consists of the tubes ; 

 their enlarged and globular extremities, which, in part, con- 

 stitute those peculiar and interesting structures, the Mal- 

 pighian bodies, and their contained granular cells. (See Plate 

 LVI1I. Jigs. 1. 6., Plate LX. figs. 2, 3.) 



Tubes. The substance of the kidney is divided into an 

 outer cortical and. an inner or medullary part. The former 

 is generally conceived to be the secreting portion of the 

 kidney, and the latter merely the tubular or conducting por- 

 tion through which the urine passes in its way to the ureter. 

 This notion of the nature of the two parts and of their mutual 

 relation is certainly erroneous, as is proved by the facts that 

 both portions of the kidney are alike formed of tubes, and 

 that all these tubes are abundantly furnished with secreting 

 cells. 



The secreting structure of the cortical part of the kidney 

 is distinguished by the large size of its tubes ; their tortuous 

 course ; the loops formed by them, not merely en the surface 

 of the kidney, but also in its interior ; by the globular en- 

 largements in which they terminate ; and by the larger size 

 &c. of their contained cells. 



The medullary part of the kidney is characterised by the 

 smaller calibre of its tubes, their straight course, the absence 

 of dilated extremities, and the frequency of the union of the 

 tubes with each other. 



The tubes then of the kidney, describing their course from 

 without inwards, commence in dilated extremities (see Plate 

 LX. figs. 2, 3.), which form part of the structure of the 

 Malpighian bodies; they afterwards take a tortuous course, 

 describing loops on the surface of the organ, as well as in its 

 interior (see Plate LIX. fig. 2. and Plate LVIII. fig. 1.), 

 until they reach the medullary part, when their course be- 

 comes straight, and where they frequently unite, especially 

 near its lower portion, in a dichotomous manner, thus forming 



