184 



UROGENITAL SYSTEM 



upper bend 



middle piece 



branches of the pelvis. The secreting tubules, on the other hand, arise quite 

 independently from the ' inner zone ' of the nephrogenetic blastema, while the 

 ' outer zone ' provides the connective-tissue framework and capsule of the organ. 



Origin of the tubules. 1 At each division of the primary collecting tubules the ' inner 

 zone ' cap becomes divided into two. The peripheral part of each moiety becomes the new 

 cap of the new branch ; but the central portion of each becomes separated off as a detached 

 oval and solid body which lies in the angle between the side branch and the main stem of the 

 duct. This is the rudiment of the capsule of Bowman, and the further phases in the development 

 of the tubule correspond exactly to those already described for the mesonephric tubules. A 

 lumen appears in the solid rudiment (fig. 230), and from the upper extremity of the vesicle 

 diverticulum passes, which abuts against, and finally opens into the collecting duct. Briefly 

 stated, the phases in the evolution of the vesicle are as follows. It first becomes comma-shaj 

 by the thickening of its outer wall. The knee formed deepens into a cleft which separates 

 the ventral part, the future capsule of Bowman, from the peripheral part, the future tubule. 

 By a second fold, which appears in the upper part of the inner wall, the tubular portion 

 becomes S-shaped, the one limb of the S opening from the capsule, the other ending in the 



collecting duct (fig. 230). Tl 

 primitive capsule of Bowman, from 

 the first hemispherical, become 

 spoon-shaped by the upgrowth of 

 its lips. Into the hollow thus pro- 

 duced the mesenchyme extends, 

 and in it, either by formation ii 

 situ, as some think, or by ingrowt 

 of a bud from a neighbouring 

 blood-vessel, a glomerulusis formed. 

 By a further great increase ii 

 length and coiling of the tubul 

 round the Malpighian body as a 

 more or less fixed point (Herring), 

 the complicated adult tubule take 

 form. The central limb of 

 S becomes the first, the periphery 

 limb the second convoluted tubule 

 while the bend of the figure, lying 

 at first in the hollow of the spe 

 elongates to form the looi 

 tubule of Henle (figs. 232, 233). 

 the primary branches of the ampulla* of the primitive pelvis continue to sprout and divide 

 it necessarily follows that the zone in which tubules are being produced is progressivel 

 displaced outwards, and thus a zone is laid down in which new tubes are formed during nearly 

 the whole of foetal life, only ceasing in the eighth month (Herring). As the kidney at an earlj 

 stage is divided into primary lobules, corresponding to groups of branching primary collectii 



1 The account in the text is founded mainly on the descriptions and figures of Herring, Schreiner, 

 and Carl Hiiber, controlled by personal examination of rabbit-material. The view that the tubule 

 have a double origin was originally advanced by Kupffer in 1865. It was substantiated by Sedgwi( 

 and adopted by Balfour. It has recently been confirmed by several observers, more especially the thn 

 named; but it should be stated that many authors have preferred the view of Kemak (1855), which w 

 maintained by Toldt and accepted by Kolliker, Waldeyer, Minot, and many others, to the effect that the 

 tubules are in their entirety produced by budding from the original diverticulum. For references to the 

 literature and for a history of opinion on this subject the reader is referred to Hiiber's paper in the 

 American Journal of Anatomy, vol. iv. 1905. 



Janosik, in the paper referred to in the note to page 182, admits the discontinuous origin of 

 secreting tubules, but describes the phases of their development differently from any other observer. 

 The process as he conceives it is one of great complexity and irregularity. The chief points are ar 

 follows : the primitive capsule and its primitive tubule connecting it with the collecting duct gives of 

 blind processes, which may become permanent tubules when the capsule is separated from the duct, ai 

 it very early is. This separation may take place in various ways, so that the primitive capsule remains 

 connected with the whole or part of its primitive tubule, or be isolated from it. The capsule now 

 acquires a new connection with the collecting duct at a point nearer the cortex, either directly by some 

 part of its own tubule, or indirectly through the medium of a different tubule. This may belong eithe 

 to another capsule, in which case a double tubule results, or may be a tubule which has lost its origins 

 capsule. Further, the capsules are often double in early stages, due to a union or to a cleaving of th 

 original rudiment. Henle's tubule cannot be recognised at an early stage as described in the text 

 apparently any loop may give rise to it. 



Henle's 

 tubule 



collecting tube 



FIG. 232. MODEL OF TWO DEVELOPING KTDNEY-TUBULES. 

 (After Stoerk.) 



On the right side the tubule is in the S-shaped stage : 

 on the left side it is beginning to coil to form the different 

 parts of the adult tubule. 



