G. Carl Huber 77 



primary loop, whieli extends toward the periphery, and numerous sec- 

 ondary loops. The distal convoluted portion is practically enclosed 

 within the coil formed by the proximal convoluted portion. The proxi- 

 mal or descending- arm of tlio loop, as the sections show, is lined nearly 

 throughout — from a little below the level of the Malpighian corpuscle to 

 near the loop proper — by a flattened epithelium, while the distal or 

 ascending arm, witli the loop itself, presents a slightly larger diameter 

 and is lined by a cubical epithelium, and on reaching the coiled portion 

 passes in front of the first part of the proximal convoluted portion, near 

 the corpuscle. Tubule B of tbis figure is from the kidney of a rabbit em- 

 bryo of 6.5 cm. length. Its length is 4.2 mm., of which 1.6 mm. falls 

 to the proximal convoluted portion, 1.8 mm. to the entire loop of Henle, 

 and .8 mm. to the remainder of the tulnilc. The disposition of the various 

 parts of this tubule is similar to that shown liy tubule A, except that the 

 distal convoluted portion is more exposed. Attention should be called 

 to the proximal arm of Henle's loop. About the upper half of this 

 presents the same diameter (and structure) as the proximal convo- 

 luted portion. This portion represents the so-called spiral portion of 

 Schachowa or the end piece (end segment) of Argutinski, and is in 

 reality the distal segment of the proximal convoluted portion. It does 

 not, so far as I have been able to observe, form a spiral ; the term spiral 

 tubule is therefore inappropriate. About the lower half of this loop 

 presents the characteristic shape and structure of the descending arm — 

 small diameter and lined by flattened epithelium. The transition from 

 one to the other is clearly shown in the figure. The loop itself, as well 

 as the ascending liml), presents a larger diameter than the thin portion 

 of the descending limb and is lined by a cubical epithelium. It may 

 here be stated that this tubule presents in a very characteristic way the 

 shape, arrangement, and structure of the several parts found in tubules, 

 the Malpighian corpuscles of which are situated in a zone of the cortex, 

 above that occupied by corpuscles and coiled portions of the tubules 

 first formed, which are nearer the medulla. 



Tulnile .1. shown in Fig. 19, represents one of the luost fully devel- 

 oped tubules from the kidney of a rabbit embryo 6.5 cm. long. It has a 

 length of 5.8 mm., of which 2.3 mm. forms the proximal convoluted 

 portion, 2.75 mm. the entire loop of Henle, and a little less than 1 mm. 

 the remainder of the tubule. This tubule I regard as one which in 

 earlier stages of development would have shown a relatively long proxi- 

 mal convoluted portion, with a short loop of Henle — a so-called atypical 

 tubule (Hamburger) — and for the following reasons: The loop of 

 Heiile reaches to near the pelvic epithelium, being separated from it l)y 



