252 



REN. 



blood after leaving the capsule, but he thinks 

 it probable that the veins form a plexus on 



Fig. 162. 



1. The anterior extremity of the kidney of the 

 Bdellostoma Forstm, of the natural size. 



a, the ureter ; b, a short uriniferous tube proceed- 

 ing from it ; d, the capsule at the extremity of the 

 tube ; /, the arterial branch entering the capsule ; 

 g, the anterior blind extremity of the ureter. 



2. Distribution of the blood-vessels in the kidney 

 of the Bdellostoma Forsteri. 



A, the ureter ; B, a uriniferous canal proceeding 

 from it ; C, section of the capsule covering the blood- 

 vessels ; D, the vascular mass injected ; a, the affe- 

 rent vessel of the same ; b, the efferent vessel ; c, an 

 artery unconnected with the vascular mass distri- 

 buted to the ureter ; d, a branch of the renal vein. 

 This figure is slightly magnified. (After Miiller.*) 



the outer surface of the tubes. It is to be 

 regretted that Miiller has not given some 

 account of the microscopic appearances pre- 

 sented by the inner surface of these tubes, 

 since without some observations on this point, 

 and particularly with reference to the charac- 

 ter of the epithelium, it is not possible to 

 form a definite notion as to the exact nature 

 of the parts in question. 



Epithelium. In examining the epithelium 

 of the kidney, it will be convenient to com- 

 mence with that of the Malpighian bodies, 

 and thence to trace this structure through the 

 tubes into the pelvis and ureter. It is scarcely 

 possible to overestimate the importance of a 

 careful study of the epithelial cells in different 

 parts of the kidney, since accurate observations 

 upon this point must form the basis of an 

 exact knowledge of the physiology of the 

 gland, and of the pathological changes to 

 which it is liable. 



Epithelium of the Malpighian bodies. With 

 reference to the epithelium of the Malpighian 

 bodies, it will suffice to recapitulate here what 

 has already been fully detailed in speaking of 

 the structure of these bodies. The epithelium 

 of the Malpighian bodies consists of two dis- 

 tinct portions : first, that which covers the 



vessels ; and, secondly, that which lines the 

 capsule. The vessels of the Malpighian tuft 

 appear to have in many instances a more or 

 less complete investment of small, delicate, 

 and transparent nucleated cells. (Fig. 100.) 

 These cells differ entirely from those on the 

 inner surface of the capsule, as well as from 

 those which line the urinary tubes. The epi- 

 thelium covering that part of the capsule which 

 is contiguous to the orifice of the tube is very 

 transparent, and clothed with vibratile cilia. 

 This ciliated epithelium covers about one-third 

 of the inner surface of the capsule ; beyond 

 this point the cilia cease, and the epithelium is 

 of excessive delicacy and translucence (figs. 

 158. and 159.), while in many instances it is 

 impossible to detect the slightest appearance 

 of epithelium beyond the line where the cilia 

 cease. The cilia in this situation have been 

 observed only in reptiles and fishes, but they 

 probably exist in all classes of Vertebrata. 



Epithelium of the uriniferous tubes. The 

 epithelium of the uriniferous tubes presents 

 itself in two distinct forms, the one kind exist- 

 ing in the convoluted tubes of the cortex, and 

 the other in the straight tubes of the medullary 

 cones. The epithelium in that part of the 

 uriniferous tubes immediately continuous with 

 the Malpighian capsule, presents the same 

 characters as that which covers the contiguous 

 portion of the capsule, consisting of delicate 

 transparent particles, which in fishes and rep- 

 tiles are furnished with vibratile cih'a. 



In the remaining portions of the tubes 

 which intervene between the neck of the 

 Malpighian capsules and the bases of the 

 medullary cones, the epithelium presents itself 

 under the form to which the term spheroidal or 

 glandular is commonly applied.* The particles 

 are of a more or less rounded form, and are 

 thus distinguished from the flattened cells of 

 the lamelliform or scaly variety of epithelium. 

 (Fig. 163.) They usually form a single layer 



Fig. 163. 



a b 



a, portion of a convoluted tube from the cortex of 

 the kidney, showing the appearance of its epithelium. 



b, portion of a straight tube with its epithelial 

 lining from a medullary cone. Magnified 200 dia- 

 meters. 



* Vide article Mucous MEMBRANE. 



