80 DcvL'lupiiK'iit and Shape oi' Uriniferous Tubules 



forced to assuiiu' the form presented by it. The Malpighian corpuscle 

 of tubule B is found in the second tier of corpuscles, while its loop of 

 Henle extends neai'ly to the pelvis of the kidney. Its entire length is 

 7.8 nun., of wliieh the ])roxinial convoluted jDortion forms 1.85 mm., 

 the entire loop 4.8 mm., the distal convoluted portion 0.55 mm., and 

 the remainder of the tubule 0.57 mm. The arrangement of the differ- 

 ent parts of the tul)ule is such that its entire course may be followed in 

 the figure ; a key is therefore dispensed with. The tubule presents only 

 a short end segment, the greater part of tlie descending tube to near the 

 loop itself forming a tubule of small diameter (12 /a to 15 /a), lined 

 throughout by a flattened epithelium, while the ascending limb with 

 the exception of the lower one-sixth is lined by a cubical epithelium 

 with faintly striated protoplasm. It is evident from the character of 

 the epithelium which lines the loop itself and the lowest part of the 

 two limbs (cells of embryonic character with relatively large, deeply 

 staining nuclei) that this portion of the loop is elongating to keep pace 

 with the enlarging and elongating Malpighian pyramid. 



The tubule shown in Fig. 20 was reconstructed from the kidney of a 

 cat embryo obtained a few days before birth; the model presents a 

 length of four feet. The tubule itself measures almost exactly 9 mm. ; 

 2.1: mm. belonging to the proximal convoluted portion, 4.85 mm. to the 

 entire loop of Henle, 1.1 mm. to the distal convoluted portion, and 

 0.55 mm. to the junctional tubule. This tul)ule I regard as showing in 

 a very typical manner the shape, arrangement, and relations of the 

 different parts of a uriniferous tubule, especially one the Malpighian 

 corpuscle of which is situated in the deeper portion of the cortex. The 

 course of the proximal convoluted portion may be ascertained from the 

 key (unshaded tubule). The curvatures of this part, as shown in the 

 key, are, for the sake of clearness, not so pronounced as in tjie actual 

 model, but are drawn with sufficient accuracy to give correctly the course 

 of this part of the tul)ule. The distal convoluted portion presents two 

 prominent loops and in its upper portion two smaller loops, in which 

 portion there may also l)e observed irregularities in the diameter of the 

 tubule. The shaded ]")ortion of the key gives the course of this portion 

 of the tubule. The coils formed by it lie over — or in front of, as shown 

 in the figure — the coil complex formed by the proximal convoluted 

 portion, the prominent loop being found a little above the Malpighian 

 corpuscle. The proximal limb of Henle's loop presents almost through- 

 out a small diameter and is lined in this portion by the characteristic 

 flattened epithelium. The end segment is short and ])resents in a typi- 

 cal manner the transition in shape and structure of the tubule as found 



