G. Carl HiilxT 91 



levels ill the niediilla. An ajjproxiniation of tlie leiifitli of uriniferous 

 tubules iiiay, therefore, be most readily made for those tubules the Mal- 

 pighian eorpuscles of which are situated in the deepest portion of the 

 cortex, the loops of Henle terminate presumal>ly near the apex of the 

 ]\ralpighian pyramid. The most fully developed tul)ule, showing a typi- 

 cal arrangement of parts, that I have reconstructed, is the one shown in 

 Fig. 20. This is from the kidney of a cat embryo, obtained a few days 

 before l)irth, and measures 9 mm. In one of the sections of this kidney 

 containing nearly the entire length of the distal limb of the loop of 

 Henle of this tubule, the width of the medulla is approximately 2.22 mm. 

 (the junction of the cortex and medulla does not form a straight line), 

 very nearly one-half the entire length of the loop of Henle (4.85 mm.). 

 In sections passing through the middle of the Malpighian pyramid of 

 the kidney of a full-grown cat, the medulla has a width of approximately 

 12 mm. Assuming, therefore, that the loops of Henle of certain of the 

 uriniferous tubules of this kidney, the Malpighian corpuscles of which 

 are situated in the deepest portion of the cortex, traverse the entire 

 wddth of the medulla, and one is justified in doing this, since loops are 

 seen in section near the very apex of the pyramid ; such a loop would 

 have a length of approximately 24 mm.; add to this the leng-fh of the 

 proximal convoluted portion, which may be given at 2.5 to 3 mm., the 

 distal convoluted portion about 1 mm., and the junctional tubule about 

 2 mm. (the width of the cortex in the sections from which the measure- 

 ments for the medulla were given varies from 2.5 mm. to 3 mm.), the 

 entire length of such a uriniferous tubule w^ould be approximately 3 cm. 

 Other tubules, the loops of Henle of which do not pass so deep down in 

 the medulla, would show a correspondingly shorter length, the shortest 

 ones measuring, if I may be allowed to estimate, 10 mm. to 12 mm. 



Y. Ebner quotes Schweiger-Seidel as stating that the proximal convo- 

 luted portion of a uriniferous tubule forms about one-fourth to one- 

 fifth of the entire uriniferous tubule, while the distal convoluted por- 

 tion, which is shorter than the proximal portion, is about one-seventh 

 of the latter's length. As concerns the relative length of the proximal 

 convoluted portion, this may be regarded as correct for tubules with 

 relatively sliort loo])s of Henle. In tubules with relatively long loops of 

 Henle it forms a relatively shorter portion — from one-eighth to one- 

 tenth of the entire tubule. So far as I am able to judge from my own 

 models and from other observations, the distal convoluted portion pre- 

 sents a length which is about one-third to one-fourth tliat of the jiroxi- 

 mal convoluted portion. If other estimates of the length of uriniferous 

 tubules or of parts thereof are to be found in the literature, they have 

 escaped my notice. 



