G. Carl TTiiber . 83 



portions may be regarded as fidly developed, is contained in a selected 

 section of a series of sections containing the whole tubule, I have in- 

 serted Figs. 21 and 22, in each of which the several parts of a single 

 uriniferous tubuli> are sketched darker than the remaining portions of 

 the sections reproduced. In Fig. 21, A and B, are reproduced portions 

 of the cortex of two sections from the series of sections from which 

 tubule B of Fig. 19 was reconstructed. A comparison of this figure with 

 that showing the reconstruction will show that the plane of section was at 

 right angles to that in which the model is reproduced. A line drawn 

 through the middle of the Malpighian corpuscle, and the proximal convo- 

 luted portion (see B, Fig. 19) shows the location of the section, a por- 

 tion of which is shown in B of Fig. 21. In this section the Malpighian 

 corpuscle, the proximal convoluted portion soon after leaving the cor- 

 puscle and two arms of a loop of it as it comes liack over the corpuscle 

 are met with. Their relation to each other and to the surrounding 

 structures may be seen from the figure. In .4 of the figure is shown 

 a portion of the lotli section further on in the series. This section 

 passes practically through the entire length of the junctional tubule 

 (leading to the periphery of the cortex) which will indicate its position 

 in the model ; also through the coils of the distal convoluted portion, 

 which is cut in cross section four times and through a long and a short 

 loop of the proximal convoluted portion, escaping the Malpighian cor- 

 puscle. In Fig. 22 is shown a portion of the cortex — about the lower 

 one-half — and the uppermost portion of the medulla of one of the sec- 

 tions from the series from which the model was made, which is shown 

 in Fig. 20. The plane of the section is nearly at right angles to the 

 model as placed on the page. The Malpighian corpuscles and tubules 

 belonging to this uriniferous tubule are sket<:'hed more deeply than other 

 parts of the figure. The section passes through about the center of 

 the Malpighian corpuscle and through the upper end of the ascending 

 limb, which may be observed as in close proximity to the corpuscle. Of 

 the five cross sections of tubules arranged nearly in a row above the 

 Malpighian corpuscle the first two and the last two are sections of the 

 distal convoluted portion, the middle one and the three nearly longi- 

 tudinal sections of tubular segments are of the ])roximal convoluted 

 portions, the lowest one just to the left of the end of the ascending 

 limb marks the end of the proximal convoluted portion, beyond which 

 the tubule becomes smaller to form the descending limb. No part of 

 the loop of Henle nor of tlie junctional tubule is shown in this section, 

 I have purposely selected for figures sections of these two uriniferous 

 tubules, since the}- represent tubules of very different form; the arrange- 



