G. Carl Hiiber 31 



with the collecting tubules and show clearly the saucer-shaped expansion 

 of the lower bend of the S-shaped structure characteristic of this stage. 



S-SHAPED Stage in the Development of the TJriniferous Tubules. 

 To characterize the S-stage of the development of the uriniferous 

 tubules more clearl}^, one may speak for convenience of description of an 

 upper S-curve, with concavity toward the collecting tubule ; an S-middle 

 piece or middle S-segment, and a lower S-curve with convexity toward 

 the collecting tubule. In considering the tubular anlage as a whole, 

 one may speak of its inner face or side, that turned toward the collecting 

 tubule, and an outer side, that turned away from the collecting tubule 

 and further of a front and, back side or face, these with reference to a 

 plane passing through the middle of a tubular anlage as in a sagittal 

 section of the same, and finally of an upper and lower portion of the 

 anlage, with reference to its attachment to the collecting tubule, which 

 would mark its upper portion. In the same way we may speak of a 

 portion of a tubular anlage as curving or growing inwards or outwards, 

 upwards or downwards, and forward or backward. In the further de- 

 scription I shall make use of these terms without further comment. In 

 this connection it needs to be recalled that renal vesicles and tubular 

 anlagen develop in connection with each of the two end branches result- 

 ing from the successive divisions which occur in the course of the devel- 

 opment of a collecting tubule. Favorable sections now and again show 

 a collecting tubule with two more or less clearly differentiated end 

 branches connected with two tubular anlagen seen in sagittal section. 

 The whole structure presents the appearance of a Y or of an anchor 

 n-ith the arms bent toward the stem of the Y or shaft of the anchor (see 

 Figs. 10 and 12). Assuming that the two tubular anlagen are in the 

 S-stage, only the left one would in reality have the shape of a Eoman S, 

 while the right one would show a mirror picture of the same. This fact 

 enables one readily to state whether any particular tubular anlage is 

 placed to the right or left of a given collecting tubule. By right or left 

 is meant the relations shown by these structures to the collecting tubule 

 to which they are attached in any given section. In the series of figures 

 showing reconstructions of tubular anlagen and early developmental 

 stages of uriniferous tubules, as given in Figs. 3, 4, 5, and 6, I have 

 for each stage of development selected a tubular anlage placed to the 

 right of a collecting tubule. It seemed to me that this would assist ma- 

 terially in tracing the successive stages and would facilitate a comparison 

 of similar stages. Tubular anlagen placed to the left of the collecting 

 tubules show the same developmental .stages which would appear in 



