88 Development and Sliapc of llrinifcrous Tubules 



give conclusive answer to this question. My own observations, based 

 on reconstructions, are therefore a confirmation of Piersol's, who states, 

 " that the relative length of the narrow part of the loop — ' descending 

 limb ' — and the broader portion vary considerably, but that almost with- 

 out exception the transition from the conspicuously narrow tube, lined 

 with the peculiar spindle epithelial cells, takes place in the descend- 

 ing limb, often at a considerable distance before the loop itself is reached, 

 so that both limbs in the vicinity of the loop itself are of the same 

 diameter and lined with the same kind of epithelium." 



The junctional tubule, the continuation of the distal convoluted por- 

 tion, after leaving the coil complex, may pass as a relatively straight 

 tubule or one showing a number of irregularities, for a shorter or greater 

 distance through the cortex, ultimately arching toward the collecting 

 tubule. The concave side of such an arch is turned toward the coil 

 complex formed by the proximal and distal convoluted portions, this 

 lying in fact between the junctional tubule and the collecting tubule to 

 Avhich a given uriniferous tubule is attached. This has also been ob- 

 served by Stoerk. 



In giving thus an outline of the course and the relations shown by 

 the different parts of uriniferous tubules, it should be understood that 

 this can be given only in a general way. For as concerns the form and 

 relations of the proximal and distal convoluted portions and their rela- 

 tion to the Malpighian corpuscle and its relation to the descending and 

 ascending limbs of Henle's loop, each tubule presents certain slight 

 differences and variations. This the models reproduced will show. No 

 two of the tubules reconstructed are exactly alike or even very nearly 

 so. The several parts of the various tubules present certain character- 

 istic relations, which, though varying more or less, are still to be recog- 

 nized. The relation of the entire uriniferous tubule to the collecting 

 tubule to which each is attached also varies, and this is quite naturally 

 more true when considering tubules showing later stages of develop- 

 ment. In the earlier stages of development, as may have been seen 

 from the figures given of these, the proximal convoluted tubule leaves 

 the Malpighian corpuscle from its inner side and passes behind the 

 upper end of the loop of Henle and, after forming several curvatures, 

 comes forward between the collecting tubule and the coil complex to 

 reach again the neighborhood of the Malpighian corpuscle and to pass 

 toward the medulla. The loop of Henle, as it leaves the coil complex, 

 is thus in front of the Malpighian corpuscle or the first part of the 

 proximal convoluted portion. As the proximal and distal convoluted 

 portions elongate and form more coils, the whole tubule is often turned 



