5'i Devclopinont and Shape of Uriniferous Tubules 



which is to form the anlage of the loop of Ilenle can be more definitely located 

 than this statement would lead one to think I believe my models will show, especially 

 those obtained from the cat and rabbit. In models of developing uriniferous tubules 

 obtained from human embryos, in which the Malpighian corpuscles develop relatively 

 early and the loop of Henle at a correspondingly later period, the portion of the 

 tubule which is to form the loop of Henle is often not easily located ; yet even from a 

 study of these models, I have gained the conviction that the loop has its anlage in 

 what has been termed the region of junction of the upper S-curve and S-middle 

 piece It is of interest to note that Stoerk states that experience shows that it is 

 icenerallv the second loop after the tubule leaves the Malpighian corpuscles, which forms 

 the anlase of the loop of Henle ; this corresponds, in the majority of the models, 

 with the^region of the junction of the upper S-curve and S-middle piece and confirms, 

 therefore, the view I have expressed. 



The majority of the observers who have considered the development of the Malpighian 

 corpuscle have in whole or in part followed Toldt, who considered Bowman's capsule 

 formed by an invagination, from one side, of the blindly ending spherical dilation of the 

 developing uriniferous tubule, mescnchvme and capillaries participating in the invagina- 

 tion and 'forming the anlage for the glomerulus. Toldt compares this process of in- 

 vagination to the pressing in of one side of a hollow rubber ball until the side pressed 

 in comes in contact with the other side. The glomerulus develops in the concavity 

 thus formed. Kolliker, Pye, .Tanosik. Nagel, Minot, Schultze, Gerhardt, and Strahl 

 may be mentioned as accepting this view, although it is not always clear from 

 their accounts to what extent they consider the fdrmation of the double walled cup, 

 the anlage of Bowman's capsule, due to an actual invagination rather than to a 

 process of growth on the part of the anlage of Bowman's capsule by means of which 

 the anlage of the glomerulus becomes surrounded. Gerhardt, for instance, states that 

 it is difficult to say whether the blind end of the uriniferous tubule plays an active 

 or a passive role in the formation of Bowman's capsule, most likely both, in that, while 

 the capillary loops grow inward, the tubule takes an active part in the formation 

 of Bowman's capsule. A more correct interpretation of the process of development 

 of Bowman's capsule and the glomerulus is given by Herring, although he missed 

 the anlage of the part which is destined to form Bowman's capsule, as has been pre- 

 viously stated. He states that " the first appearance of the cavity of Bowman's 

 capsule is a narrow slit and never a vesicle in the human kidney. Toldt's description 

 of the driving in of one wall by capillaries is not an accurate one. At this stage 

 there are no^ capillaries in the "glomerulus." "The further growth in size of the 

 glomerulus may be described as an invagination, but it is not an invagination of the 

 kind usually supposed. None of it takes place at the expense of the other side as 

 occurs in Toldfs illustration of the rubber ball. It is rather an increase in size by 

 proliferation of its own constituents ; the base remains in the same position and is wide 

 at first but gradually narrows, the narrowing being brought about by the formative 

 action of large cells covering it." The formation of the lower S-curve, the anlage of 

 Bowman's capsule, has been correctly given by Schreiner, as has been stated, and in 

 this my own observations confirm him. Bv way of summary it may be stated that the 

 two layers of the lip-shaped fold, which is separated from the outer, lower part of the 

 renal vesicle, and which forms the anlage of the lower S-curve, are from the beginning 

 nearly in contact, the fold presenting a slight concavity above and a corresponding 

 convexity below. As the anlage of the lower S-curve proceeds in its development, it 

 increases in size and assumes the shape of the bowl of a spoon, with a distinct 

 border except where attached to the tabular portion of the anlage ; the handle of the 

 spoon, which must be thought of as bent so as to form the greater part of an S. At 

 rbout this time, a small amount of mesenchyme may be found in the concavity of the 

 lower S-curve, at first without capillaries, these growing in from without. In its 

 further development, this double walled structure, which represents the segment of a 

 sphere, changes 1o a hemisohere by a growing upwards of the border, the mesenchyme 

 proliferating and the capillaries increasing in number so as to fill the concavity as 

 this develops. By a further arowing upwards and a turning in of the border and by 

 the formation of'a fold on tlie inner layer, the hemispherical structure changes to a 

 spherical structure, Bowman's capsule and the glomerulus being thus completed. That 

 Bowman's capsule with its outer and inner layer is developed by growing upwards 

 and ultimately by a turning in of the border of the structure with shallow concavity 

 as seen in tlie lower S-curve when this is first recognized, both sections and recon- 

 structions seem to me to show. In sections of a developing Bowman's capsule, both 

 the inner and outer laver for a short distance from the border and along its entire 

 leno-th show undifferentiated embrvonic cells indicating the growing zone. This may 

 be seen in the sketches shown in Fig. 3. This view of the development of the Mal- 

 pighian corpuscle is the one taken by Stoerk, who has given correctly the main fea- 

 tures of its development, braving out of consideration the anl.is:e of the lower S-curve. 

 the formation of which he hardly considers, and the formation of the fold which 

 assists in transforming the hemispherical into a spherical structure: this fold he 

 recognized but believes it to be developed from the middle S-piece of the primary S, 

 which, as has been stated, he regards as being taken up into the anlage of Bowman's 

 capsule, while the primary S-stage is changing into the secondary S ; in my own account, 

 T have endeavored to show that it develops as a fold of the inner layer of the anlage 

 ■of Bowman's capsule independent of the S-middle piece. 



Throughout the period in which new tubules are formed, new genera- 

 tions of uriniferous tubules develop outside (toward the periphery of the 

 kidney) of those previously formed, the latter thus coming to lie relatively 



